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 $239.25   11.303%   $266.2924   $266.29   $266.30   $266.30  
  Purchase #2 $84.44   12.641%   $95.1141   $95.11   $95.10   $95.10  
  Purchase #3 $232.33   12.239%   $260.7649   $260.76   $260.75   $260.80  
  Purchase #4 $194.73   13.645%   $221.3009   $221.30   $221.30   $221.30  
  Purchase #5 $105.69   10.259%   $116.5327   $116.53   $116.55   $116.50  
  Purchase #6 $226.60   5.463%   $238.9792   $238.98   $239.00   $239.00  
  Purchase #7 $116.75   9.296%   $127.6031   $127.60   $127.60   $127.60  
  7 purchase totals = $1,199.79       $1,326.5873   $1,326.57   $1,326.60   $1,326.60