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 $227.46   11.512%   $253.6452   $253.65   $253.65   $253.60  
  Purchase #2 $87.85   4.200%   $91.5397   $91.54   $91.55   $91.50  
  Purchase #3 $43.40   10.358%   $47.8954   $47.90   $47.90   $47.90  
  Purchase #4 $204.51   10.354%   $225.685   $225.69   $225.70   $225.70  
  Purchase #5 $175.75   8.608%   $190.8786   $190.88   $190.90   $190.90  
  Purchase #6 $40.78   12.760%   $45.9835   $45.98   $46.00   $46.00  
  Purchase #7 $25.80   11.351%   $28.7286   $28.73   $28.75   $28.70  
  7 purchase totals = $805.55       $884.3560   $884.37   $884.45   $884.30