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 $190.25   13.440%   $215.8196   $215.82   $215.80   $215.80  
  Purchase #2 $88.72   10.832%   $98.3302   $98.33   $98.35   $98.30  
  Purchase #3 $213.59   7.246%   $229.0667   $229.07   $229.05   $229.10  
  Purchase #4 $238.68   4.828%   $250.2035   $250.20   $250.20   $250.20  
  Purchase #5 $223.99   4.323%   $233.6731   $233.67   $233.65   $233.70  
  Purchase #6 $53.53   10.696%   $59.2556   $59.26   $59.25   $59.30  
  Purchase #7 $166.93   8.708%   $181.4663   $181.47   $181.45   $181.50  
  7 purchase totals = $1,175.69       $1,267.8150   $1,267.82   $1,267.75   $1,267.90