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 $167.26   10.376%   $184.6149   $184.61   $184.60   $184.60  
  Purchase #2 $92.97   3.738%   $96.4452   $96.45   $96.45   $96.40  
  Purchase #3 $149.76   10.807%   $165.9446   $165.94   $165.95   $165.90  
  Purchase #4 $123.92   9.187%   $135.3045   $135.30   $135.30   $135.30  
  Purchase #5 $185.40   8.208%   $200.6176   $200.62   $200.60   $200.60  
  Purchase #6 $238.44   9.553%   $261.2182   $261.22   $261.20   $261.20  
  Purchase #7 $85.28   11.149%   $94.7879   $94.79   $94.80   $94.80  
  7 purchase totals = $1,043.03       $1,138.9329   $1,138.93   $1,138.90   $1,138.80