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 $116.63   12.647%   $131.3802   $131.38   $131.40   $131.40  
  Purchase #2 $188.84   7.438%   $202.8859   $202.89   $202.90   $202.90  
  Purchase #3 $165.80   12.251%   $186.1122   $186.11   $186.10   $186.10  
  Purchase #4 $206.61   13.423%   $234.3433   $234.34   $234.35   $234.30  
  Purchase #5 $61.95   4.862%   $64.962   $64.96   $64.95   $65.00  
  Purchase #6 $190.56   5.293%   $200.6463   $200.65   $200.65   $200.60  
  Purchase #7 $18.93   12.709%   $21.3358   $21.34   $21.35   $21.30  
  7 purchase totals = $949.32       $1,041.6657   $1,041.67   $1,041.70   $1,041.60