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 $176.78   11.774%   $197.5941   $197.59   $197.60   $197.60  
  Purchase #2 $22.60   4.401%   $23.5946   $23.59   $23.60   $23.60  
  Purchase #3 $85.42   8.775%   $92.9156   $92.92   $92.90   $92.90  
  Purchase #4 $52.48   11.150%   $58.3315   $58.33   $58.35   $58.30  
  Purchase #5 $217.30   11.352%   $241.9679   $241.97   $241.95   $242.00  
  Purchase #6 $185.49   10.109%   $204.2412   $204.24   $204.25   $204.20  
  Purchase #7 $191.39   5.864%   $202.6131   $202.61   $202.60   $202.60  
  7 purchase totals = $931.46       $1,021.2580   $1,021.25   $1,021.25   $1,021.20