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 $86.25   11.813%   $96.4387   $96.44   $96.45   $96.40  
  Purchase #2 $30.68   13.131%   $34.7086   $34.71   $34.70   $34.70  
  Purchase #3 $193.84   8.625%   $210.5587   $210.56   $210.55   $210.60  
  Purchase #4 $86.31   3.481%   $89.3145   $89.31   $89.30   $89.30  
  Purchase #5 $68.53   9.840%   $75.2734   $75.27   $75.25   $75.30  
  Purchase #6 $91.69   9.321%   $100.2364   $100.24   $100.25   $100.20  
  Purchase #7 $66.80   11.676%   $74.5996   $74.60   $74.60   $74.60  
  7 purchase totals = $624.10       $681.1299   $681.13   $681.10   $681.10