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 $60.43   5.838%   $63.9579   $63.96   $63.95   $64.00  
  Purchase #2 $248.86   3.449%   $257.4432   $257.44   $257.45   $257.40  
  Purchase #3 $139.25   5.477%   $146.8767   $146.88   $146.90   $146.90  
  Purchase #4 $48.70   7.585%   $52.3939   $52.39   $52.40   $52.40  
  Purchase #5 $86.32   5.339%   $90.9286   $90.93   $90.95   $90.90  
  Purchase #6 $125.57   9.596%   $137.6197   $137.62   $137.60   $137.60  
  Purchase #7 $44.37   8.438%   $48.1139   $48.11   $48.10   $48.10  
  7 purchase totals = $753.50       $797.3339   $797.33   $797.35   $797.30