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 $166.41   10.763%   $184.3207   $184.32   $184.30   $184.30  
  Purchase #2 $58.34   11.462%   $65.0269   $65.03   $65.05   $65.00  
  Purchase #3 $47.40   10.119%   $52.1964   $52.20   $52.20   $52.20  
  Purchase #4 $12.79   8.374%   $13.861   $13.86   $13.85   $13.90  
  Purchase #5 $89.71   6.298%   $95.3599   $95.36   $95.35   $95.40  
  Purchase #6 $157.36   10.692%   $174.1849   $174.18   $174.20   $174.20  
  Purchase #7 $250.28   12.796%   $282.3058   $282.31   $282.30   $282.30  
  7 purchase totals = $782.29       $867.2556   $867.26   $867.25   $867.30