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 $37.39   11.244%   $41.5941   $41.59   $41.60   $41.60  
  Purchase #2 $67.81   10.269%   $74.7734   $74.77   $74.75   $74.80  
  Purchase #3 $188.40   7.753%   $203.0067   $203.01   $203.00   $203.00  
  Purchase #4 $97.87   9.681%   $107.3448   $107.34   $107.35   $107.30  
  Purchase #5 $207.55   13.754%   $236.0964   $236.10   $236.10   $236.10  
  Purchase #6 $220.37   6.813%   $235.3838   $235.38   $235.40   $235.40  
  Purchase #7 $76.46   7.109%   $81.8955   $81.90   $81.90   $81.90  
  7 purchase totals = $895.85       $980.0947   $980.09   $980.10   $980.10