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 $143.80   9.255%   $157.1087   $157.11   $157.10   $157.10  
  Purchase #2 $97.75   3.188%   $100.8663   $100.87   $100.85   $100.90  
  Purchase #3 $108.52   8.290%   $117.5163   $117.52   $117.50   $117.50  
  Purchase #4 $100.57   13.593%   $114.2405   $114.24   $114.25   $114.20  
  Purchase #5 $64.97   10.476%   $71.7763   $71.78   $71.80   $71.80  
  Purchase #6 $231.58   5.724%   $244.8356   $244.84   $244.85   $244.80  
  Purchase #7 $6.64   6.478%   $7.0701   $7.07   $7.05   $7.10  
  7 purchase totals = $753.83       $813.4138   $813.43   $813.40   $813.40