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 $67.50   8.478%   $73.2227   $73.22   $73.20   $73.20  
  Purchase #2 $31.40   13.658%   $35.6886   $35.69   $35.70   $35.70  
  Purchase #3 $173.45   6.649%   $184.9827   $184.98   $185.00   $185.00  
  Purchase #4 $244.47   3.305%   $252.5497   $252.55   $252.55   $252.50  
  Purchase #5 $99.29   5.287%   $104.5395   $104.54   $104.55   $104.50  
  Purchase #6 $49.58   4.158%   $51.6415   $51.64   $51.65   $51.60  
  Purchase #7 $31.28   10.299%   $34.5015   $34.50   $34.50   $34.50  
  7 purchase totals = $696.97       $737.1262   $737.12   $737.15   $737.00