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 $79.58   11.467%   $88.7054   $88.71   $88.70   $88.70  
  Purchase #2 $96.39   6.277%   $102.4404   $102.44   $102.45   $102.40  
  Purchase #3 $69.27   9.761%   $76.0314   $76.03   $76.05   $76.00  
  Purchase #4 $236.27   13.620%   $268.45   $268.45   $268.45   $268.50  
  Purchase #5 $83.55   9.368%   $91.377   $91.38   $91.40   $91.40  
  Purchase #6 $194.68   10.358%   $214.845   $214.85   $214.85   $214.80  
  Purchase #7 $79.27   8.193%   $85.7646   $85.76   $85.75   $85.80  
  7 purchase totals = $839.01       $927.6138   $927.62   $927.65   $927.60