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 $238.75   12.560%   $268.737   $268.74   $268.75   $268.70  
  Purchase #2 $101.60   5.694%   $107.3851   $107.39   $107.40   $107.40  
  Purchase #3 $203.92   10.740%   $225.821   $225.82   $225.80   $225.80  
  Purchase #4 $43.71   13.344%   $49.5427   $49.54   $49.55   $49.50  
  Purchase #5 $22.83   4.585%   $23.8768   $23.88   $23.90   $23.90  
  Purchase #6 $241.31   11.242%   $268.4381   $268.44   $268.45   $268.40  
  Purchase #7 $112.98   11.146%   $125.5728   $125.57   $125.55   $125.60  
  7 purchase totals = $965.10       $1,069.3735   $1,069.38   $1,069.40   $1,069.30