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 $180.58   11.286%   $200.9603   $200.96   $200.95   $201.00  
  Purchase #2 $108.73   5.431%   $114.6351   $114.64   $114.65   $114.60  
  Purchase #3 $113.90   5.868%   $120.5837   $120.58   $120.60   $120.60  
  Purchase #4 $36.29   6.676%   $38.7127   $38.71   $38.70   $38.70  
  Purchase #5 $142.96   10.558%   $158.0537   $158.05   $158.05   $158.10  
  Purchase #6 $29.73   4.442%   $31.0506   $31.05   $31.05   $31.10  
  Purchase #7 $48.81   11.176%   $54.265   $54.27   $54.25   $54.30  
  7 purchase totals = $661.00       $718.2611   $718.26   $718.25   $718.40