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 $64.61   11.152%   $71.8153   $71.82   $71.80   $71.80  
  Purchase #2 $200.66   7.612%   $215.9342   $215.93   $215.95   $215.90  
  Purchase #3 $233.37   11.763%   $260.8213   $260.82   $260.80   $260.80  
  Purchase #4 $95.99   9.788%   $105.3855   $105.39   $105.40   $105.40  
  Purchase #5 $187.70   6.414%   $199.7391   $199.74   $199.75   $199.70  
  Purchase #6 $219.27   9.421%   $239.9274   $239.93   $239.95   $239.90  
  Purchase #7 $202.83   9.618%   $222.3382   $222.34   $222.35   $222.30  
  7 purchase totals = $1,204.43       $1,315.9610   $1,315.97   $1,316.00   $1,315.80