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 $224.26   6.687%   $239.2563   $239.26   $239.25   $239.30  
  Purchase #2 $33.28   8.633%   $36.1531   $36.15   $36.15   $36.20  
  Purchase #3 $165.65   4.623%   $173.308   $173.31   $173.30   $173.30  
  Purchase #4 $31.26   8.349%   $33.8699   $33.87   $33.85   $33.90  
  Purchase #5 $240.82   7.354%   $258.5299   $258.53   $258.55   $258.50  
  Purchase #6 $239.90   11.846%   $268.3186   $268.32   $268.30   $268.30  
  Purchase #7 $240.35   4.706%   $251.6609   $251.66   $251.65   $251.70  
  7 purchase totals = $1,175.52       $1,261.0967   $1,261.10   $1,261.05   $1,261.20