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 $221.61   10.207%   $244.2297   $244.23   $244.25   $244.20  
  Purchase #2 $126.81   4.744%   $132.8259   $132.83   $132.85   $132.80  
  Purchase #3 $62.52   11.550%   $69.7411   $69.74   $69.75   $69.70  
  Purchase #4 $64.82   8.788%   $70.5164   $70.52   $70.50   $70.50  
  Purchase #5 $111.77   12.220%   $125.4283   $125.43   $125.45   $125.40  
  Purchase #6 $176.42   13.873%   $200.8947   $200.89   $200.90   $200.90  
  Purchase #7 $113.65   13.539%   $129.0371   $129.04   $129.05   $129.00  
  7 purchase totals = $877.60       $972.6732   $972.68   $972.75   $972.50