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 $188.91   10.420%   $208.5944   $208.59   $208.60   $208.60  
  Purchase #2 $80.65   5.520%   $85.1019   $85.10   $85.10   $85.10  
  Purchase #3 $64.69   4.412%   $67.5441   $67.54   $67.55   $67.50  
  Purchase #4 $63.33   7.845%   $68.2982   $68.30   $68.30   $68.30  
  Purchase #5 $223.74   13.803%   $254.6228   $254.62   $254.60   $254.60  
  Purchase #6 $80.74   8.133%   $87.3066   $87.31   $87.30   $87.30  
  Purchase #7 $180.95   7.739%   $194.9537   $194.95   $194.95   $195.00  
  7 purchase totals = $883.01       $966.4217   $966.41   $966.40   $966.40