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 $73.66   3.565%   $76.286   $76.29   $76.30   $76.30  
  Purchase #2 $95.81   7.437%   $102.9354   $102.94   $102.95   $102.90  
  Purchase #3 $138.51   5.323%   $145.8829   $145.88   $145.90   $145.90  
  Purchase #4 $178.62   4.523%   $186.699   $186.70   $186.70   $186.70  
  Purchase #5 $226.77   6.548%   $241.6189   $241.62   $241.60   $241.60  
  Purchase #6 $161.91   4.544%   $169.2672   $169.27   $169.25   $169.30  
  Purchase #7 $54.53   3.197%   $56.2733   $56.27   $56.25   $56.30  
  7 purchase totals = $929.81       $978.9627   $978.97   $978.95   $979.00