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 $119.83   3.110%   $123.5567   $123.56   $123.55   $123.60  
  Purchase #2 $45.52   11.315%   $50.6706   $50.67   $50.65   $50.70  
  Purchase #3 $213.45   4.742%   $223.5718   $223.57   $223.55   $223.60  
  Purchase #4 $216.53   9.445%   $236.9813   $236.98   $237.00   $237.00  
  Purchase #5 $79.31   6.684%   $84.6111   $84.61   $84.60   $84.60  
  Purchase #6 $193.94   12.294%   $217.783   $217.78   $217.80   $217.80  
  Purchase #7 $107.86   4.684%   $112.9122   $112.91   $112.90   $112.90  
  7 purchase totals = $976.44       $1,050.0867   $1,050.08   $1,050.05   $1,050.20