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 $36.43   10.178%   $40.1378   $40.14   $40.15   $40.10  
  Purchase #2 $105.82   9.450%   $115.82   $115.82   $115.80   $115.80  
  Purchase #3 $163.85   11.731%   $183.0712   $183.07   $183.05   $183.10  
  Purchase #4 $196.97   13.212%   $222.9937   $222.99   $223.00   $223.00  
  Purchase #5 $200.35   3.377%   $207.1158   $207.12   $207.10   $207.10  
  Purchase #6 $109.60   7.185%   $117.4748   $117.47   $117.45   $117.50  
  Purchase #7 $231.46   7.729%   $249.3495   $249.35   $249.35   $249.30  
  7 purchase totals = $1,044.48       $1,135.9628   $1,135.96   $1,135.90   $1,135.90