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 $227.77   6.829%   $243.3244   $243.32   $243.30   $243.30  
  Purchase #2 $161.54   7.641%   $173.8833   $173.88   $173.90   $173.90  
  Purchase #3 $32.48   8.787%   $35.334   $35.33   $35.35   $35.30  
  Purchase #4 $249.80   13.452%   $283.4031   $283.40   $283.40   $283.40  
  Purchase #5 $199.63   6.524%   $212.6539   $212.65   $212.65   $212.70  
  Purchase #6 $115.54   8.198%   $125.012   $125.01   $125.00   $125.00  
  Purchase #7 $167.98   6.358%   $178.6602   $178.66   $178.65   $178.70  
  7 purchase totals = $1,154.74       $1,252.2709   $1,252.25   $1,252.25   $1,252.30