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 $54.76   11.453%   $61.0317   $61.03   $61.05   $61.00  
  Purchase #2 $45.59   8.841%   $49.6206   $49.62   $49.60   $49.60  
  Purchase #3 $44.49   13.239%   $50.38   $50.38   $50.40   $50.40  
  Purchase #4 $141.61   12.433%   $159.2164   $159.22   $159.20   $159.20  
  Purchase #5 $222.78   7.690%   $239.9118   $239.91   $239.90   $239.90  
  Purchase #6 $235.51   5.198%   $247.7518   $247.75   $247.75   $247.80  
  Purchase #7 $91.35   9.457%   $99.989   $99.99   $100.00   $100.00  
  7 purchase totals = $836.09       $907.9013   $907.90   $907.90   $907.90