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 $30.80   11.701%   $34.4039   $34.40   $34.40   $34.40  
  Purchase #2 $151.98   4.147%   $158.2826   $158.28   $158.30   $158.30  
  Purchase #3 $160.47   9.862%   $176.2956   $176.30   $176.30   $176.30  
  Purchase #4 $44.53   13.307%   $50.4556   $50.46   $50.45   $50.50  
  Purchase #5 $155.69   10.179%   $171.5377   $171.54   $171.55   $171.50  
  Purchase #6 $53.59   8.704%   $58.2545   $58.25   $58.25   $58.30  
  Purchase #7 $206.96   13.552%   $235.0072   $235.01   $235.00   $235.00  
  7 purchase totals = $804.02       $884.2371   $884.24   $884.25   $884.30