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 $250.39   5.817%   $264.9552   $264.96   $264.95   $265.00  
  Purchase #2 $80.47   7.586%   $86.5745   $86.57   $86.55   $86.60  
  Purchase #3 $209.81   5.688%   $221.744   $221.74   $221.75   $221.70  
  Purchase #4 $82.81   12.761%   $93.3774   $93.38   $93.40   $93.40  
  Purchase #5 $125.77   11.144%   $139.7858   $139.79   $139.80   $139.80  
  Purchase #6 $170.37   7.419%   $183.0098   $183.01   $183.00   $183.00  
  Purchase #7 $126.45   7.105%   $135.4343   $135.43   $135.45   $135.40  
  7 purchase totals = $1,046.07       $1,124.8810   $1,124.88   $1,124.90   $1,124.90