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 $118.45   12.370%   $133.1023   $133.10   $133.10   $133.10  
  Purchase #2 $143.85   7.730%   $154.9696   $154.97   $154.95   $155.00  
  Purchase #3 $221.77   3.571%   $229.6894   $229.69   $229.70   $229.70  
  Purchase #4 $140.59   4.318%   $146.6607   $146.66   $146.65   $146.70  
  Purchase #5 $94.37   13.223%   $106.8485   $106.85   $106.85   $106.80  
  Purchase #6 $41.80   8.180%   $45.2192   $45.22   $45.20   $45.20  
  Purchase #7 $221.84   5.123%   $233.2049   $233.20   $233.20   $233.20  
  7 purchase totals = $982.67       $1,049.6946   $1,049.69   $1,049.65   $1,049.70