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 $249.97   7.606%   $268.9827   $268.98   $269.00   $269.00  
  Purchase #2 $194.84   9.686%   $213.7122   $213.71   $213.70   $213.70  
  Purchase #3 $107.59   9.674%   $117.9983   $118.00   $118.00   $118.00  
  Purchase #4 $78.95   10.813%   $87.4869   $87.49   $87.50   $87.50  
  Purchase #5 $103.96   11.305%   $115.7127   $115.71   $115.70   $115.70  
  Purchase #6 $112.32   11.594%   $125.3424   $125.34   $125.35   $125.30  
  Purchase #7 $75.68   12.565%   $85.1892   $85.19   $85.20   $85.20  
  7 purchase totals = $923.31       $1,014.4244   $1,014.42   $1,014.45   $1,014.40