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 $244.25   8.495%   $264.999   $265.00   $265.00   $265.00  
  Purchase #2 $45.36   6.373%   $48.2508   $48.25   $48.25   $48.30  
  Purchase #3 $171.82   10.854%   $190.4693   $190.47   $190.45   $190.50  
  Purchase #4 $82.46   13.465%   $93.5632   $93.56   $93.55   $93.60  
  Purchase #5 $48.49   11.400%   $54.0179   $54.02   $54.00   $54.00  
  Purchase #6 $176.62   4.302%   $184.2182   $184.22   $184.20   $184.20  
  Purchase #7 $190.77   13.793%   $217.0829   $217.08   $217.10   $217.10  
  7 purchase totals = $959.77       $1,052.6013   $1,052.60   $1,052.55   $1,052.70