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 $163.96   12.130%   $183.8483   $183.85   $183.85   $183.80  
  Purchase #2 $248.67   10.846%   $275.6407   $275.64   $275.65   $275.60  
  Purchase #3 $41.72   10.367%   $46.0451   $46.05   $46.05   $46.00  
  Purchase #4 $181.60   8.829%   $197.6335   $197.63   $197.65   $197.60  
  Purchase #5 $55.76   6.869%   $59.5902   $59.59   $59.60   $59.60  
  Purchase #6 $115.83   6.804%   $123.7111   $123.71   $123.70   $123.70  
  Purchase #7 $161.70   9.721%   $177.4189   $177.42   $177.40   $177.40  
  7 purchase totals = $969.24       $1,063.8878   $1,063.89   $1,063.90   $1,063.70