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 $204.80   11.577%   $228.5097   $228.51   $228.50   $228.50  
  Purchase #2 $136.97   11.674%   $152.9599   $152.96   $152.95   $153.00  
  Purchase #3 $46.97   4.164%   $48.9258   $48.93   $48.95   $48.90  
  Purchase #4 $76.66   7.427%   $82.3535   $82.35   $82.35   $82.40  
  Purchase #5 $166.69   12.834%   $188.083   $188.08   $188.10   $188.10  
  Purchase #6 $52.73   11.255%   $58.6648   $58.66   $58.65   $58.70  
  Purchase #7 $186.84   3.578%   $193.5251   $193.53   $193.55   $193.50  
  7 purchase totals = $871.66       $953.0218   $953.02   $953.05   $953.10