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 $248.67   10.814%   $275.5612   $275.56   $275.55   $275.60  
  Purchase #2 $88.47   3.657%   $91.7053   $91.71   $91.70   $91.70  
  Purchase #3 $89.69   5.509%   $94.631   $94.63   $94.65   $94.60  
  Purchase #4 $195.97   10.611%   $216.7644   $216.76   $216.75   $216.80  
  Purchase #5 $210.42   12.335%   $236.3753   $236.38   $236.40   $236.40  
  Purchase #6 $199.62   5.252%   $210.104   $210.10   $210.10   $210.10  
  Purchase #7 $66.52   5.298%   $70.0442   $70.04   $70.05   $70.00  
  7 purchase totals = $1,099.36       $1,195.1854   $1,195.18   $1,195.20   $1,195.20