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 $34.46   5.443%   $36.3357   $36.34   $36.35   $36.30  
  Purchase #2 $126.30   3.198%   $130.3391   $130.34   $130.35   $130.30  
  Purchase #3 $72.95   12.280%   $81.9083   $81.91   $81.90   $81.90  
  Purchase #4 $166.26   3.217%   $171.6086   $171.61   $171.60   $171.60  
  Purchase #5 $126.62   10.667%   $140.1266   $140.13   $140.15   $140.10  
  Purchase #6 $167.75   5.565%   $177.0853   $177.09   $177.10   $177.10  
  Purchase #7 $192.87   11.580%   $215.2043   $215.20   $215.20   $215.20  
  7 purchase totals = $887.21       $952.6079   $952.62   $952.65   $952.50