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 $218.56   9.635%   $239.6183   $239.62   $239.60   $239.60  
  Purchase #2 $166.25   8.162%   $179.8193   $179.82   $179.80   $179.80  
  Purchase #3 $60.61   5.383%   $63.8726   $63.87   $63.85   $63.90  
  Purchase #4 $76.63   10.239%   $84.4761   $84.48   $84.50   $84.50  
  Purchase #5 $51.56   6.570%   $54.9475   $54.95   $54.95   $54.90  
  Purchase #6 $148.98   11.780%   $166.5298   $166.53   $166.55   $166.50  
  Purchase #7 $215.42   8.743%   $234.2542   $234.25   $234.25   $234.30  
  7 purchase totals = $938.01       $1,023.5178   $1,023.52   $1,023.50   $1,023.50