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 $106.70   11.645%   $119.1252   $119.13   $119.15   $119.10  
  Purchase #2 $221.45   13.188%   $250.6548   $250.65   $250.65   $250.70  
  Purchase #3 $233.55   13.145%   $264.2501   $264.25   $264.25   $264.30  
  Purchase #4 $216.90   9.347%   $237.1736   $237.17   $237.15   $237.20  
  Purchase #5 $123.66   6.800%   $132.0689   $132.07   $132.05   $132.10  
  Purchase #6 $48.91   11.621%   $54.5938   $54.59   $54.60   $54.60  
  Purchase #7 $54.56   7.860%   $58.8484   $58.85   $58.85   $58.80  
  7 purchase totals = $1,005.73       $1,116.7148   $1,116.71   $1,116.70   $1,116.80