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 $68.65   7.410%   $73.737   $73.74   $73.75   $73.70  
  Purchase #2 $127.92   11.739%   $142.9365   $142.94   $142.95   $142.90  
  Purchase #3 $128.39   9.368%   $140.4176   $140.42   $140.40   $140.40  
  Purchase #4 $159.64   3.382%   $165.039   $165.04   $165.05   $165.00  
  Purchase #5 $152.55   5.828%   $161.4406   $161.44   $161.45   $161.40  
  Purchase #6 $149.25   8.552%   $162.0139   $162.01   $162.00   $162.00  
  Purchase #7 $71.92   8.618%   $78.1181   $78.12   $78.10   $78.10  
  7 purchase totals = $858.32       $923.7027   $923.71   $923.70   $923.50