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 $245.56   8.742%   $267.0269   $267.03   $267.05   $267.00  
  Purchase #2 $171.72   6.274%   $182.4937   $182.49   $182.50   $182.50  
  Purchase #3 $57.27   13.158%   $64.8056   $64.81   $64.80   $64.80  
  Purchase #4 $186.84   9.576%   $204.7318   $204.73   $204.75   $204.70  
  Purchase #5 $54.66   3.298%   $56.4627   $56.46   $56.45   $56.50  
  Purchase #6 $59.67   11.738%   $66.6741   $66.67   $66.65   $66.70  
  Purchase #7 $206.66   7.510%   $222.1802   $222.18   $222.20   $222.20  
  7 purchase totals = $982.38       $1,064.3750   $1,064.37   $1,064.40   $1,064.40