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 $241.29   10.824%   $267.4072   $267.41   $267.40   $267.40  
  Purchase #2 $246.37   5.186%   $259.1467   $259.15   $259.15   $259.10  
  Purchase #3 $153.61   7.134%   $164.5685   $164.57   $164.55   $164.60  
  Purchase #4 $5.46   12.218%   $6.1271   $6.13   $6.15   $6.10  
  Purchase #5 $58.80   12.301%   $66.033   $66.03   $66.05   $66.00  
  Purchase #6 $18.35   11.613%   $20.481   $20.48   $20.50   $20.50  
  Purchase #7 $137.81   10.286%   $151.9851   $151.99   $152.00   $152.00  
  7 purchase totals = $861.69       $935.7486   $935.76   $935.80   $935.70