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 $237.82   7.629%   $255.9633   $255.96   $255.95   $256.00  
  Purchase #2 $50.36   4.781%   $52.7677   $52.77   $52.75   $52.80  
  Purchase #3 $30.81   9.133%   $33.6239   $33.62   $33.60   $33.60  
  Purchase #4 $206.46   13.183%   $233.6776   $233.68   $233.70   $233.70  
  Purchase #5 $162.90   10.394%   $179.8318   $179.83   $179.85   $179.80  
  Purchase #6 $245.73   12.805%   $277.1957   $277.20   $277.20   $277.20  
  Purchase #7 $95.63   9.807%   $105.0084   $105.01   $105.00   $105.00  
  7 purchase totals = $1,029.71       $1,138.0684   $1,138.07   $1,138.05   $1,138.10