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 $61.43   6.143%   $65.2036   $65.20   $65.20   $65.20  
  Purchase #2 $71.89   10.452%   $79.4039   $79.40   $79.40   $79.40  
  Purchase #3 $229.93   13.272%   $260.4463   $260.45   $260.45   $260.40  
  Purchase #4 $54.98   12.137%   $61.6529   $61.65   $61.65   $61.70  
  Purchase #5 $44.52   5.731%   $47.0714   $47.07   $47.05   $47.10  
  Purchase #6 $91.77   7.601%   $98.7454   $98.75   $98.75   $98.70  
  Purchase #7 $106.57   4.862%   $111.7514   $111.75   $111.75   $111.80  
  7 purchase totals = $661.09       $724.2749   $724.27   $724.25   $724.30