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 $166.99   3.640%   $173.0684   $173.07   $173.05   $173.10  
  Purchase #2 $151.96   4.697%   $159.0976   $159.10   $159.10   $159.10  
  Purchase #3 $122.37   3.462%   $126.6064   $126.61   $126.60   $126.60  
  Purchase #4 $86.87   4.874%   $91.104   $91.10   $91.10   $91.10  
  Purchase #5 $31.84   12.691%   $35.8808   $35.88   $35.90   $35.90  
  Purchase #6 $193.77   8.283%   $209.82   $209.82   $209.80   $209.80  
  Purchase #7 $25.75   6.175%   $27.3401   $27.34   $27.35   $27.30  
  7 purchase totals = $779.55       $822.9173   $822.92   $822.90   $822.90