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 $144.86   10.618%   $160.2412   $160.24   $160.25   $160.20  
  Purchase #2 $84.47   13.163%   $95.5888   $95.59   $95.60   $95.60  
  Purchase #3 $201.76   10.189%   $222.3173   $222.32   $222.30   $222.30  
  Purchase #4 $154.39   4.858%   $161.8903   $161.89   $161.90   $161.90  
  Purchase #5 $179.25   4.833%   $187.9132   $187.91   $187.90   $187.90  
  Purchase #6 $131.53   3.230%   $135.7784   $135.78   $135.80   $135.80  
  Purchase #7 $63.99   10.809%   $70.9067   $70.91   $70.90   $70.90  
  7 purchase totals = $960.25       $1,034.6359   $1,034.64   $1,034.65   $1,034.60