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 $204.81   4.141%   $213.2912   $213.29   $213.30   $213.30  
  Purchase #2 $223.69   7.306%   $240.0328   $240.03   $240.05   $240.00  
  Purchase #3 $58.95   4.800%   $61.7796   $61.78   $61.80   $61.80  
  Purchase #4 $88.76   9.688%   $97.3591   $97.36   $97.35   $97.40  
  Purchase #5 $165.57   8.645%   $179.8835   $179.88   $179.90   $179.90  
  Purchase #6 $69.28   10.344%   $76.4463   $76.45   $76.45   $76.40  
  Purchase #7 $30.90   6.342%   $32.8597   $32.86   $32.85   $32.90  
  7 purchase totals = $841.96       $901.6522   $901.65   $901.70   $901.70