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 $196.87   10.783%   $218.0985   $218.10   $218.10   $218.10  
  Purchase #2 $233.96   5.803%   $247.5367   $247.54   $247.55   $247.50  
  Purchase #3 $113.43   5.281%   $119.4202   $119.42   $119.40   $119.40  
  Purchase #4 $199.58   9.431%   $218.4024   $218.40   $218.40   $218.40  
  Purchase #5 $214.30   9.168%   $233.947   $233.95   $233.95   $233.90  
  Purchase #6 $142.47   7.523%   $153.188   $153.19   $153.20   $153.20  
  Purchase #7 $143.87   5.168%   $151.3052   $151.31   $151.30   $151.30  
  7 purchase totals = $1,244.48       $1,341.8980   $1,341.91   $1,341.90   $1,341.80