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 $31.91   10.492%   $35.258   $35.26   $35.25   $35.30  
  Purchase #2 $168.58   9.844%   $185.175   $185.18   $185.20   $185.20  
  Purchase #3 $36.28   10.277%   $40.0085   $40.01   $40.00   $40.00  
  Purchase #4 $63.62   12.458%   $71.5458   $71.55   $71.55   $71.50  
  Purchase #5 $157.59   10.599%   $174.293   $174.29   $174.30   $174.30  
  Purchase #6 $73.78   5.213%   $77.6262   $77.63   $77.65   $77.60  
  Purchase #7 $226.73   12.446%   $254.9488   $254.95   $254.95   $254.90  
  7 purchase totals = $758.49       $838.8553   $838.87   $838.90   $838.80