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 $227.64   8.747%   $247.5517   $247.55   $247.55   $247.60  
  Purchase #2 $149.96   3.460%   $155.1486   $155.15   $155.15   $155.10  
  Purchase #3 $248.80   6.335%   $264.5615   $264.56   $264.55   $264.60  
  Purchase #4 $15.67   5.245%   $16.4919   $16.49   $16.50   $16.50  
  Purchase #5 $205.64   11.719%   $229.739   $229.74   $229.75   $229.70  
  Purchase #6 $53.98   9.233%   $58.964   $58.96   $58.95   $59.00  
  Purchase #7 $228.90   3.755%   $237.4952   $237.50   $237.50   $237.50  
  7 purchase totals = $1,130.59       $1,209.9519   $1,209.95   $1,209.95   $1,210.00