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 $59.59   6.556%   $63.4967   $63.50   $63.50   $63.50  
  Purchase #2 $169.36   7.441%   $181.9621   $181.96   $181.95   $182.00  
  Purchase #3 $166.91   3.151%   $172.1693   $172.17   $172.15   $172.20  
  Purchase #4 $111.93   3.804%   $116.1878   $116.19   $116.20   $116.20  
  Purchase #5 $60.50   4.448%   $63.191   $63.19   $63.20   $63.20  
  Purchase #6 $131.80   5.169%   $138.6127   $138.61   $138.60   $138.60  
  Purchase #7 $174.25   5.198%   $183.3075   $183.31   $183.30   $183.30  
  7 purchase totals = $874.34       $918.9271   $918.93   $918.90   $919.00