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 $245.78   6.468%   $261.6771   $261.68   $261.70   $261.70  
  Purchase #2 $44.43   7.600%   $47.8067   $47.81   $47.80   $47.80  
  Purchase #3 $246.82   7.131%   $264.4207   $264.42   $264.40   $264.40  
  Purchase #4 $210.72   10.552%   $232.9552   $232.96   $232.95   $233.00  
  Purchase #5 $59.70   9.526%   $65.387   $65.39   $65.40   $65.40  
  Purchase #6 $240.59   9.732%   $264.0042   $264.00   $264.00   $264.00  
  Purchase #7 $113.92   12.550%   $128.217   $128.22   $128.20   $128.20  
  7 purchase totals = $1,161.96       $1,264.4679   $1,264.48   $1,264.45   $1,264.50