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 $245.53   6.213%   $260.7848   $260.78   $260.80   $260.80  
  Purchase #2 $187.50   5.522%   $197.8538   $197.85   $197.85   $197.90  
  Purchase #3 $239.51   13.476%   $271.7864   $271.79   $271.80   $271.80  
  Purchase #4 $61.89   8.185%   $66.9557   $66.96   $66.95   $67.00  
  Purchase #5 $189.60   6.546%   $202.0112   $202.01   $202.00   $202.00  
  Purchase #6 $234.87   10.230%   $258.8972   $258.90   $258.90   $258.90  
  Purchase #7 $130.43   5.514%   $137.6219   $137.62   $137.60   $137.60  
  7 purchase totals = $1,289.33       $1,395.9110   $1,395.91   $1,395.90   $1,396.00