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 $59.67   9.594%   $65.3947   $65.39   $65.40   $65.40  
  Purchase #2 $141.76   4.753%   $148.4979   $148.50   $148.50   $148.50  
  Purchase #3 $57.96   5.547%   $61.175   $61.18   $61.20   $61.20  
  Purchase #4 $17.68   13.409%   $20.0507   $20.05   $20.05   $20.10  
  Purchase #5 $50.27   7.792%   $54.187   $54.19   $54.20   $54.20  
  Purchase #6 $126.80   12.830%   $143.0684   $143.07   $143.05   $143.10  
  Purchase #7 $242.76   10.318%   $267.808   $267.81   $267.80   $267.80  
  7 purchase totals = $696.90       $760.1817   $760.19   $760.20   $760.30