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 $57.30   3.303%   $59.1926   $59.19   $59.20   $59.20  
  Purchase #2 $146.98   13.590%   $166.9546   $166.95   $166.95   $167.00  
  Purchase #3 $250.28   3.332%   $258.6193   $258.62   $258.60   $258.60  
  Purchase #4 $73.38   5.523%   $77.4328   $77.43   $77.45   $77.40  
  Purchase #5 $241.63   10.517%   $267.0422   $267.04   $267.05   $267.00  
  Purchase #6 $45.62   9.801%   $50.0912   $50.09   $50.10   $50.10  
  Purchase #7 $155.91   9.788%   $171.1705   $171.17   $171.15   $171.20  
  7 purchase totals = $971.10       $1,050.5032   $1,050.49   $1,050.50   $1,050.50