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 $203.96   11.133%   $226.6669   $226.67   $226.65   $226.70  
  Purchase #2 $42.48   9.141%   $46.3631   $46.36   $46.35   $46.40  
  Purchase #3 $154.61   4.592%   $161.7097   $161.71   $161.70   $161.70  
  Purchase #4 $61.69   6.858%   $65.9207   $65.92   $65.90   $65.90  
  Purchase #5 $203.71   7.473%   $218.9332   $218.93   $218.95   $218.90  
  Purchase #6 $64.65   9.756%   $70.9573   $70.96   $70.95   $71.00  
  Purchase #7 $88.81   10.294%   $97.9521   $97.95   $97.95   $98.00  
  7 purchase totals = $819.91       $888.5030   $888.50   $888.45   $888.60