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 $230.75   8.676%   $250.7699   $250.77   $250.75   $250.80  
  Purchase #2 $60.88   5.460%   $64.204   $64.20   $64.20   $64.20  
  Purchase #3 $177.89   7.825%   $191.8099   $191.81   $191.80   $191.80  
  Purchase #4 $244.74   8.210%   $264.8332   $264.83   $264.85   $264.80  
  Purchase #5 $92.69   4.277%   $96.6544   $96.65   $96.65   $96.70  
  Purchase #6 $206.39   5.118%   $216.953   $216.95   $216.95   $217.00  
  Purchase #7 $240.51   3.634%   $249.2501   $249.25   $249.25   $249.30  
  7 purchase totals = $1,253.85       $1,334.4745   $1,334.46   $1,334.45   $1,334.60