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 $246.96   8.224%   $267.27   $267.27   $267.25   $267.30  
  Purchase #2 $104.46   3.146%   $107.7463   $107.75   $107.75   $107.70  
  Purchase #3 $62.73   9.208%   $68.5062   $68.51   $68.50   $68.50  
  Purchase #4 $159.58   9.873%   $175.3353   $175.34   $175.35   $175.30  
  Purchase #5 $177.66   8.326%   $192.452   $192.45   $192.45   $192.50  
  Purchase #6 $160.98   4.796%   $168.7006   $168.70   $168.70   $168.70  
  Purchase #7 $240.94   3.648%   $249.7295   $249.73   $249.75   $249.70  
  7 purchase totals = $1,153.31       $1,229.7399   $1,229.75   $1,229.75   $1,229.70