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 $107.33   11.754%   $119.9456   $119.95   $119.95   $119.90  
  Purchase #2 $33.54   4.147%   $34.9309   $34.93   $34.95   $34.90  
  Purchase #3 $104.30   12.444%   $117.2791   $117.28   $117.30   $117.30  
  Purchase #4 $7.96   4.292%   $8.3016   $8.30   $8.30   $8.30  
  Purchase #5 $240.98   7.575%   $259.2342   $259.23   $259.25   $259.20  
  Purchase #6 $61.74   5.713%   $65.2672   $65.27   $65.25   $65.30  
  Purchase #7 $106.57   8.761%   $115.9066   $115.91   $115.90   $115.90  
  7 purchase totals = $662.42       $720.8652   $720.87   $720.90   $720.80