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 $208.56   12.494%   $234.6175   $234.62   $234.60   $234.60  
  Purchase #2 $34.33   9.460%   $37.5776   $37.58   $37.60   $37.60  
  Purchase #3 $245.96   4.290%   $256.5117   $256.51   $256.50   $256.50  
  Purchase #4 $55.84   8.806%   $60.7573   $60.76   $60.75   $60.80  
  Purchase #5 $24.49   6.709%   $26.133   $26.13   $26.15   $26.10  
  Purchase #6 $115.45   3.144%   $119.0797   $119.08   $119.10   $119.10  
  Purchase #7 $162.34   9.667%   $178.0334   $178.03   $178.05   $178.00  
  7 purchase totals = $846.97       $912.7102   $912.71   $912.75   $912.70