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 $51.37   11.478%   $57.2662   $57.27   $57.25   $57.30  
  Purchase #2 $200.25   12.189%   $224.6585   $224.66   $224.65   $224.70  
  Purchase #3 $50.66   8.163%   $54.7954   $54.80   $54.80   $54.80  
  Purchase #4 $156.57   9.874%   $172.0297   $172.03   $172.05   $172.00  
  Purchase #5 $200.60   6.749%   $214.1385   $214.14   $214.15   $214.10  
  Purchase #6 $79.44   8.408%   $86.1193   $86.12   $86.10   $86.10  
  Purchase #7 $200.76   12.208%   $225.2688   $225.27   $225.25   $225.30  
  7 purchase totals = $939.65       $1,034.2764   $1,034.29   $1,034.25   $1,034.30