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 $92.49   11.418%   $103.0505   $103.05   $103.05   $103.10  
  Purchase #2 $233.60   3.303%   $241.3158   $241.32   $241.30   $241.30  
  Purchase #3 $113.73   10.690%   $125.8877   $125.89   $125.90   $125.90  
  Purchase #4 $16.69   6.821%   $17.8284   $17.83   $17.85   $17.80  
  Purchase #5 $181.76   6.824%   $194.1633   $194.16   $194.15   $194.20  
  Purchase #6 $191.65   7.464%   $205.9548   $205.95   $205.95   $206.00  
  Purchase #7 $152.75   8.521%   $165.7658   $165.77   $165.75   $165.80  
  7 purchase totals = $982.67       $1,053.9663   $1,053.97   $1,053.95   $1,054.10