Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $107.68   3.566%   $111.5199   $111.52   $111.50   $111.50  
  Purchase #2 $136.65   11.873%   $152.8745   $152.87   $152.85   $152.90  
  Purchase #3 $211.45   7.645%   $227.6154   $227.62   $227.60   $227.60  
  Purchase #4 $194.69   12.761%   $219.5344   $219.53   $219.55   $219.50  
  Purchase #5 $195.92   5.657%   $207.0032   $207.00   $207.00   $207.00  
  Purchase #6 $189.58   4.274%   $197.6826   $197.68   $197.70   $197.70  
  Purchase #7 $233.79   11.216%   $260.0119   $260.01   $260.00   $260.00  
  7 purchase totals = $1,269.76       $1,376.2419   $1,376.23   $1,376.20   $1,376.20