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 $85.67   10.623%   $94.7707   $94.77   $94.75   $94.80  
  Purchase #2 $221.92   9.313%   $242.5874   $242.59   $242.60   $242.60  
  Purchase #3 $75.79   11.367%   $84.405   $84.41   $84.40   $84.40  
  Purchase #4 $133.61   5.555%   $141.032   $141.03   $141.05   $141.00  
  Purchase #5 $145.53   9.531%   $159.4005   $159.40   $159.40   $159.40  
  Purchase #6 $118.81   4.852%   $124.5747   $124.57   $124.55   $124.60  
  Purchase #7 $98.68   8.532%   $107.0994   $107.10   $107.10   $107.10  
  7 purchase totals = $880.01       $953.8697   $953.87   $953.85   $953.90