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 $149.92   8.593%   $162.8026   $162.80   $162.80   $162.80  
  Purchase #2 $71.29   3.757%   $73.9684   $73.97   $73.95   $74.00  
  Purchase #3 $83.30   10.180%   $91.7799   $91.78   $91.80   $91.80  
  Purchase #4 $65.71   6.383%   $69.9043   $69.90   $69.90   $69.90  
  Purchase #5 $198.90   4.527%   $207.9042   $207.90   $207.90   $207.90  
  Purchase #6 $164.86   9.477%   $180.4838   $180.48   $180.50   $180.50  
  Purchase #7 $68.79   9.187%   $75.1097   $75.11   $75.10   $75.10  
  7 purchase totals = $802.77       $861.9529   $861.94   $861.95   $862.00