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 $24.98   6.426%   $26.5852   $26.59   $26.60   $26.60  
  Purchase #2 $156.49   8.464%   $169.7353   $169.74   $169.75   $169.70  
  Purchase #3 $173.28   7.625%   $186.4926   $186.49   $186.50   $186.50  
  Purchase #4 $10.75   7.561%   $11.5628   $11.56   $11.55   $11.60  
  Purchase #5 $241.44   5.871%   $255.6149   $255.61   $255.60   $255.60  
  Purchase #6 $62.63   5.544%   $66.1022   $66.10   $66.10   $66.10  
  Purchase #7 $121.84   5.750%   $128.8458   $128.85   $128.85   $128.80  
  7 purchase totals = $791.41       $844.9388   $844.94   $844.95   $844.90