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 $62.44   6.109%   $66.2545   $66.25   $66.25   $66.30  
  Purchase #2 $227.56   12.104%   $255.1039   $255.10   $255.10   $255.10  
  Purchase #3 $176.84   4.417%   $184.651   $184.65   $184.65   $184.70  
  Purchase #4 $90.45   4.758%   $94.7536   $94.75   $94.75   $94.80  
  Purchase #5 $227.95   12.245%   $255.8625   $255.86   $255.85   $255.90  
  Purchase #6 $110.56   8.718%   $120.1986   $120.20   $120.20   $120.20  
  Purchase #7 $67.87   12.299%   $76.2173   $76.22   $76.20   $76.20  
  7 purchase totals = $963.67       $1,053.0414   $1,053.03   $1,053.00   $1,053.20