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 $49.29   6.228%   $52.3598   $52.36   $52.35   $52.40  
  Purchase #2 $62.58   6.570%   $66.6915   $66.69   $66.70   $66.70  
  Purchase #3 $153.61   12.815%   $173.2951   $173.30   $173.30   $173.30  
  Purchase #4 $236.28   6.113%   $250.7238   $250.72   $250.70   $250.70  
  Purchase #5 $46.47   7.367%   $49.8934   $49.89   $49.90   $49.90  
  Purchase #6 $47.63   5.854%   $50.4183   $50.42   $50.40   $50.40  
  Purchase #7 $204.36   13.116%   $231.1639   $231.16   $231.15   $231.20  
  7 purchase totals = $800.22       $874.5458   $874.54   $874.50   $874.60