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 $93.73   11.314%   $104.3346   $104.33   $104.35   $104.30  
  Purchase #2 $215.25   8.302%   $233.1201   $233.12   $233.10   $233.10  
  Purchase #3 $40.82   11.589%   $45.5506   $45.55   $45.55   $45.60  
  Purchase #4 $183.73   8.503%   $199.3526   $199.35   $199.35   $199.40  
  Purchase #5 $79.90   5.377%   $84.1962   $84.20   $84.20   $84.20  
  Purchase #6 $241.67   10.654%   $267.4175   $267.42   $267.40   $267.40  
  Purchase #7 $96.95   11.259%   $107.8656   $107.87   $107.85   $107.90  
  7 purchase totals = $952.05       $1,041.8372   $1,041.84   $1,041.80   $1,041.90