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 $55.47   11.504%   $61.8513   $61.85   $61.85   $61.90  
  Purchase #2 $182.56   13.554%   $207.3042   $207.30   $207.30   $207.30  
  Purchase #3 $243.61   9.571%   $266.9259   $266.93   $266.95   $266.90  
  Purchase #4 $77.84   8.262%   $84.2711   $84.27   $84.25   $84.30  
  Purchase #5 $104.86   11.162%   $116.5645   $116.56   $116.55   $116.60  
  Purchase #6 $192.54   6.655%   $205.3535   $205.35   $205.35   $205.40  
  Purchase #7 $21.30   6.572%   $22.6998   $22.70   $22.70   $22.70  
  7 purchase totals = $878.18       $964.9703   $964.96   $964.95   $965.10