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 $63.63   10.293%   $70.1794   $70.18   $70.20   $70.20  
  Purchase #2 $202.61   7.251%   $217.3013   $217.30   $217.30   $217.30  
  Purchase #3 $58.76   7.655%   $63.2581   $63.26   $63.25   $63.30  
  Purchase #4 $32.80   10.796%   $36.3411   $36.34   $36.35   $36.30  
  Purchase #5 $56.52   9.575%   $61.9318   $61.93   $61.95   $61.90  
  Purchase #6 $11.28   10.332%   $12.4454   $12.45   $12.45   $12.40  
  Purchase #7 $214.31   9.308%   $234.258   $234.26   $234.25   $234.30  
  7 purchase totals = $639.91       $695.7151   $695.72   $695.75   $695.70