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 $88.31   10.181%   $97.3008   $97.30   $97.30   $97.30  
  Purchase #2 $101.43   6.621%   $108.1457   $108.15   $108.15   $108.10  
  Purchase #3 $8.43   12.861%   $9.5142   $9.51   $9.50   $9.50  
  Purchase #4 $61.40   12.837%   $69.2819   $69.28   $69.30   $69.30  
  Purchase #5 $132.53   12.281%   $148.806   $148.81   $148.80   $148.80  
  Purchase #6 $204.41   5.459%   $215.5687   $215.57   $215.55   $215.60  
  Purchase #7 $225.48   9.633%   $247.2005   $247.20   $247.20   $247.20  
  7 purchase totals = $821.99       $895.8178   $895.82   $895.80   $895.80