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 $57.39   8.703%   $62.3847   $62.38   $62.40   $62.40  
  Purchase #2 $228.86   9.121%   $249.7343   $249.73   $249.75   $249.70  
  Purchase #3 $209.78   8.139%   $226.854   $226.85   $226.85   $226.90  
  Purchase #4 $191.97   9.736%   $210.6602   $210.66   $210.65   $210.70  
  Purchase #5 $111.65   10.421%   $123.285   $123.29   $123.30   $123.30  
  Purchase #6 $179.60   5.193%   $188.9266   $188.93   $188.95   $188.90  
  Purchase #7 $147.33   9.492%   $161.3146   $161.31   $161.30   $161.30  
  7 purchase totals = $1,126.58       $1,223.1594   $1,223.15   $1,223.20   $1,223.20