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 $46.43   8.201%   $50.2377   $50.24   $50.25   $50.20  
  Purchase #2 $117.67   6.539%   $125.3644   $125.36   $125.35   $125.40  
  Purchase #3 $16.95   3.388%   $17.5243   $17.52   $17.50   $17.50  
  Purchase #4 $7.74   7.661%   $8.333   $8.33   $8.35   $8.30  
  Purchase #5 $66.91   3.378%   $69.1702   $69.17   $69.15   $69.20  
  Purchase #6 $191.92   5.263%   $202.0207   $202.02   $202.00   $202.00  
  Purchase #7 $31.55   3.208%   $32.5621   $32.56   $32.55   $32.60  
  7 purchase totals = $479.17       $505.2124   $505.20   $505.15   $505.20