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 $163.59   12.561%   $184.1385   $184.14   $184.15   $184.10  
  Purchase #2 $169.91   7.443%   $182.5564   $182.56   $182.55   $182.60  
  Purchase #3 $165.47   13.179%   $187.2773   $187.28   $187.30   $187.30  
  Purchase #4 $16.82   12.629%   $18.9442   $18.94   $18.95   $18.90  
  Purchase #5 $185.63   3.234%   $191.6333   $191.63   $191.65   $191.60  
  Purchase #6 $99.47   10.241%   $109.6567   $109.66   $109.65   $109.70  
  Purchase #7 $129.57   8.387%   $140.437   $140.44   $140.45   $140.40  
  7 purchase totals = $930.46       $1,014.6434   $1,014.65   $1,014.70   $1,014.60