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 $53.93   4.199%   $56.1945   $56.19   $56.20   $56.20  
  Purchase #2 $106.28   4.113%   $110.6513   $110.65   $110.65   $110.70  
  Purchase #3 $236.95   12.385%   $266.2963   $266.30   $266.30   $266.30  
  Purchase #4 $16.78   13.867%   $19.1069   $19.11   $19.10   $19.10  
  Purchase #5 $49.94   11.190%   $55.5283   $55.53   $55.55   $55.50  
  Purchase #6 $153.81   4.764%   $161.1375   $161.14   $161.15   $161.10  
  Purchase #7 $212.62   8.208%   $230.0718   $230.07   $230.05   $230.10  
  7 purchase totals = $830.31       $898.9866   $898.99   $899.00   $899.00