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 $234.66   13.791%   $267.022   $267.02   $267.00   $267.00  
  Purchase #2 $69.76   9.135%   $76.1326   $76.13   $76.15   $76.10  
  Purchase #3 $160.67   7.345%   $172.4712   $172.47   $172.45   $172.50  
  Purchase #4 $242.47   5.533%   $255.8859   $255.89   $255.90   $255.90  
  Purchase #5 $22.95   11.190%   $25.5181   $25.52   $25.50   $25.50  
  Purchase #6 $88.99   4.355%   $92.8655   $92.87   $92.85   $92.90  
  Purchase #7 $200.99   13.471%   $228.0654   $228.07   $228.05   $228.10  
  7 purchase totals = $1,020.49       $1,117.9607   $1,117.97   $1,117.90   $1,118.00