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 $238.62   6.822%   $254.8987   $254.90   $254.90   $254.90  
  Purchase #2 $9.40   3.470%   $9.7262   $9.73   $9.75   $9.70  
  Purchase #3 $87.53   6.463%   $93.1871   $93.19   $93.20   $93.20  
  Purchase #4 $60.51   13.481%   $68.6674   $68.67   $68.65   $68.70  
  Purchase #5 $247.26   8.548%   $268.3958   $268.40   $268.40   $268.40  
  Purchase #6 $178.60   6.782%   $190.7127   $190.71   $190.70   $190.70  
  Purchase #7 $247.43   5.483%   $260.9966   $261.00   $261.00   $261.00  
  7 purchase totals = $1,069.35       $1,146.5845   $1,146.60   $1,146.60   $1,146.60