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 $46.69   7.660%   $50.2665   $50.27   $50.25   $50.30  
  Purchase #2 $242.87   9.533%   $266.0228   $266.02   $266.00   $266.00  
  Purchase #3 $117.79   5.689%   $124.4911   $124.49   $124.50   $124.50  
  Purchase #4 $230.28   4.466%   $240.5643   $240.56   $240.55   $240.60  
  Purchase #5 $59.94   11.331%   $66.7318   $66.73   $66.75   $66.70  
  Purchase #6 $245.35   8.656%   $266.5875   $266.59   $266.60   $266.60  
  Purchase #7 $42.83   7.859%   $46.196   $46.20   $46.20   $46.20  
  7 purchase totals = $985.75       $1,060.8600   $1,060.86   $1,060.85   $1,060.90