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 $84.77   10.712%   $93.8506   $93.85   $93.85   $93.90  
  Purchase #2 $21.57   5.857%   $22.8334   $22.83   $22.85   $22.80  
  Purchase #3 $171.98   4.773%   $180.1886   $180.19   $180.20   $180.20  
  Purchase #4 $109.62   12.128%   $122.9147   $122.91   $122.90   $122.90  
  Purchase #5 $87.77   9.174%   $95.822   $95.82   $95.80   $95.80  
  Purchase #6 $5.81   10.512%   $6.4207   $6.42   $6.40   $6.40  
  Purchase #7 $149.37   3.163%   $154.0946   $154.09   $154.10   $154.10  
  7 purchase totals = $630.89       $676.1246   $676.11   $676.10   $676.10