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 $128.42   13.840%   $146.1933   $146.19   $146.20   $146.20  
  Purchase #2 $166.96   8.393%   $180.973   $180.97   $180.95   $181.00  
  Purchase #3 $161.82   11.172%   $179.8985   $179.90   $179.90   $179.90  
  Purchase #4 $157.80   10.111%   $173.7552   $173.76   $173.75   $173.80  
  Purchase #5 $135.52   10.719%   $150.0464   $150.05   $150.05   $150.00  
  Purchase #6 $45.43   6.423%   $48.348   $48.35   $48.35   $48.30  
  Purchase #7 $200.74   13.435%   $227.7094   $227.71   $227.70   $227.70  
  7 purchase totals = $996.69       $1,106.9238   $1,106.93   $1,106.90   $1,106.90