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 $195.64   11.558%   $218.2521   $218.25   $218.25   $218.30  
  Purchase #2 $79.25   9.231%   $86.5656   $86.57   $86.55   $86.60  
  Purchase #3 $84.95   4.416%   $88.7014   $88.70   $88.70   $88.70  
  Purchase #4 $161.29   5.115%   $169.54   $169.54   $169.55   $169.50  
  Purchase #5 $226.72   9.748%   $248.8207   $248.82   $248.80   $248.80  
  Purchase #6 $60.30   10.205%   $66.4536   $66.45   $66.45   $66.50  
  Purchase #7 $41.48   13.521%   $47.0885   $47.09   $47.10   $47.10  
  7 purchase totals = $849.63       $925.4219   $925.42   $925.40   $925.50