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 $162.29   6.819%   $173.3566   $173.36   $173.35   $173.40  
  Purchase #2 $179.60   8.871%   $195.5323   $195.53   $195.55   $195.50  
  Purchase #3 $61.90   10.108%   $68.1569   $68.16   $68.15   $68.20  
  Purchase #4 $163.36   12.793%   $184.2586   $184.26   $184.25   $184.30  
  Purchase #5 $8.91   5.198%   $9.3731   $9.37   $9.35   $9.40  
  Purchase #6 $147.49   4.748%   $154.4928   $154.49   $154.50   $154.50  
  Purchase #7 $137.69   7.265%   $147.6932   $147.69   $147.70   $147.70  
  7 purchase totals = $861.24       $932.8635   $932.86   $932.85   $933.00