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 $61.39   6.113%   $65.1428   $65.14   $65.15   $65.10  
  Purchase #2 $104.71   11.550%   $116.804   $116.80   $116.80   $116.80  
  Purchase #3 $205.95   13.554%   $233.8645   $233.86   $233.85   $233.90  
  Purchase #4 $179.73   9.735%   $197.2267   $197.23   $197.25   $197.20  
  Purchase #5 $17.35   11.722%   $19.3838   $19.38   $19.40   $19.40  
  Purchase #6 $71.73   4.355%   $74.8538   $74.85   $74.85   $74.90  
  Purchase #7 $174.26   8.844%   $189.6716   $189.67   $189.65   $189.70  
  7 purchase totals = $815.12       $896.9472   $896.93   $896.95   $897.00