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 $111.65   12.843%   $125.9892   $125.99   $126.00   $126.00  
  Purchase #2 $49.74   5.168%   $52.3106   $52.31   $52.30   $52.30  
  Purchase #3 $137.63   4.389%   $143.6706   $143.67   $143.65   $143.70  
  Purchase #4 $159.88   9.272%   $174.7041   $174.70   $174.70   $174.70  
  Purchase #5 $99.70   7.138%   $106.8166   $106.82   $106.80   $106.80  
  Purchase #6 $216.85   7.652%   $233.4434   $233.44   $233.45   $233.40  
  Purchase #7 $101.97   5.166%   $107.2378   $107.24   $107.25   $107.20  
  7 purchase totals = $877.42       $944.1723   $944.17   $944.15   $944.10