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 $226.33   12.462%   $254.5352   $254.54   $254.55   $254.50  
  Purchase #2 $244.96   6.742%   $261.4752   $261.48   $261.50   $261.50  
  Purchase #3 $189.87   4.308%   $198.0496   $198.05   $198.05   $198.00  
  Purchase #4 $64.77   3.351%   $66.9404   $66.94   $66.95   $66.90  
  Purchase #5 $190.75   6.225%   $202.6242   $202.62   $202.60   $202.60  
  Purchase #6 $6.32   3.537%   $6.5435   $6.54   $6.55   $6.50  
  Purchase #7 $67.30   6.672%   $71.7903   $71.79   $71.80   $71.80  
  7 purchase totals = $990.30       $1,061.9584   $1,061.96   $1,062.00   $1,061.80