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 $111.73   13.431%   $126.7365   $126.74   $126.75   $126.70  
  Purchase #2 $159.29   8.721%   $173.1817   $173.18   $173.20   $173.20  
  Purchase #3 $183.46   8.138%   $198.39   $198.39   $198.40   $198.40  
  Purchase #4 $146.70   6.822%   $156.7079   $156.71   $156.70   $156.70  
  Purchase #5 $122.34   8.578%   $132.8343   $132.83   $132.85   $132.80  
  Purchase #6 $191.92   3.256%   $198.1689   $198.17   $198.15   $198.20  
  Purchase #7 $39.80   11.318%   $44.3046   $44.30   $44.30   $44.30  
  7 purchase totals = $955.24       $1,030.3239   $1,030.32   $1,030.35   $1,030.30