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 $123.59   13.739%   $140.57   $140.57   $140.55   $140.60  
  Purchase #2 $208.88   6.453%   $222.359   $222.36   $222.35   $222.40  
  Purchase #3 $86.92   8.590%   $94.3864   $94.39   $94.40   $94.40  
  Purchase #4 $184.82   5.181%   $194.3955   $194.40   $194.40   $194.40  
  Purchase #5 $194.75   9.810%   $213.855   $213.86   $213.85   $213.90  
  Purchase #6 $233.97   4.588%   $244.7045   $244.70   $244.70   $244.70  
  Purchase #7 $88.84   6.292%   $94.4298   $94.43   $94.45   $94.40  
  7 purchase totals = $1,121.77       $1,204.7002   $1,204.71   $1,204.70   $1,204.80