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 $246.65   11.843%   $275.8608   $275.86   $275.85   $275.90  
  Purchase #2 $223.44   8.141%   $241.6303   $241.63   $241.65   $241.60  
  Purchase #3 $223.70   9.431%   $244.7971   $244.80   $244.80   $244.80  
  Purchase #4 $130.68   8.110%   $141.2781   $141.28   $141.30   $141.30  
  Purchase #5 $68.35   6.485%   $72.7825   $72.78   $72.80   $72.80  
  Purchase #6 $173.61   6.636%   $185.1308   $185.13   $185.15   $185.10  
  Purchase #7 $239.80   12.131%   $268.8901   $268.89   $268.90   $268.90  
  7 purchase totals = $1,306.23       $1,430.3697   $1,430.37   $1,430.45   $1,430.40