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 $184.61   11.775%   $206.3478   $206.35   $206.35   $206.30  
  Purchase #2 $98.82   5.266%   $104.0239   $104.02   $104.00   $104.00  
  Purchase #3 $187.36   12.516%   $210.81   $210.81   $210.80   $210.80  
  Purchase #4 $222.99   11.347%   $248.2927   $248.29   $248.30   $248.30  
  Purchase #5 $99.35   4.836%   $104.1546   $104.15   $104.15   $104.20  
  Purchase #6 $211.70   7.357%   $227.2748   $227.27   $227.25   $227.30  
  Purchase #7 $142.74   3.211%   $147.3234   $147.32   $147.30   $147.30  
  7 purchase totals = $1,147.57       $1,248.2272   $1,248.21   $1,248.15   $1,248.20