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 $61.41   11.270%   $68.3309   $68.33   $68.35   $68.30  
  Purchase #2 $184.92   11.510%   $206.2043   $206.20   $206.20   $206.20  
  Purchase #3 $77.64   4.649%   $81.2495   $81.25   $81.25   $81.20  
  Purchase #4 $104.27   7.841%   $112.4458   $112.45   $112.45   $112.40  
  Purchase #5 $153.64   10.721%   $170.1117   $170.11   $170.10   $170.10  
  Purchase #6 $77.98   12.635%   $87.8328   $87.83   $87.85   $87.80  
  Purchase #7 $248.73   3.165%   $256.6023   $256.60   $256.60   $256.60  
  7 purchase totals = $908.59       $982.7773   $982.77   $982.80   $982.60