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 $88.45   7.570%   $95.1457   $95.15   $95.15   $95.10  
  Purchase #2 $41.98   10.277%   $46.2943   $46.29   $46.30   $46.30  
  Purchase #3 $123.34   11.632%   $137.6869   $137.69   $137.70   $137.70  
  Purchase #4 $98.54   4.280%   $102.7575   $102.76   $102.75   $102.80  
  Purchase #5 $23.64   13.454%   $26.8205   $26.82   $26.80   $26.80  
  Purchase #6 $181.93   9.858%   $199.8647   $199.86   $199.85   $199.90  
  Purchase #7 $101.28   10.418%   $111.8314   $111.83   $111.85   $111.80  
  7 purchase totals = $659.16       $720.4010   $720.40   $720.40   $720.40