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 $132.81   8.662%   $144.314   $144.31   $144.30   $144.30  
  Purchase #2 $241.42   12.227%   $270.9384   $270.94   $270.95   $270.90  
  Purchase #3 $98.34   7.184%   $105.4047   $105.40   $105.40   $105.40  
  Purchase #4 $44.89   13.861%   $51.1122   $51.11   $51.10   $51.10  
  Purchase #5 $105.43   13.647%   $119.818   $119.82   $119.80   $119.80  
  Purchase #6 $175.84   5.414%   $185.36   $185.36   $185.35   $185.40  
  Purchase #7 $231.29   5.806%   $244.7187   $244.72   $244.70   $244.70  
  7 purchase totals = $1,030.02       $1,121.6660   $1,121.66   $1,121.60   $1,121.60