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 $76.28   10.579%   $84.3497   $84.35   $84.35   $84.30  
  Purchase #2 $220.89   13.501%   $250.7124   $250.71   $250.70   $250.70  
  Purchase #3 $224.80   5.519%   $237.2067   $237.21   $237.20   $237.20  
  Purchase #4 $74.77   11.359%   $83.2631   $83.26   $83.25   $83.30  
  Purchase #5 $69.69   9.303%   $76.1733   $76.17   $76.15   $76.20  
  Purchase #6 $234.65   4.345%   $244.8455   $244.85   $244.85   $244.80  
  Purchase #7 $55.58   5.524%   $58.6502   $58.65   $58.65   $58.70  
  7 purchase totals = $956.66       $1,035.2009   $1,035.20   $1,035.15   $1,035.20