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 $28.26   7.568%   $30.3987   $30.40   $30.40   $30.40  
  Purchase #2 $191.64   9.298%   $209.4587   $209.46   $209.45   $209.50  
  Purchase #3 $176.75   3.826%   $183.5125   $183.51   $183.50   $183.50  
  Purchase #4 $12.41   8.544%   $13.4703   $13.47   $13.45   $13.50  
  Purchase #5 $160.74   12.385%   $180.6476   $180.65   $180.65   $180.60  
  Purchase #6 $97.36   3.330%   $100.6021   $100.60   $100.60   $100.60  
  Purchase #7 $175.61   10.286%   $193.6732   $193.67   $193.65   $193.70  
  7 purchase totals = $842.77       $911.7631   $911.76   $911.70   $911.80