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 $44.32   9.491%   $48.5264   $48.53   $48.55   $48.50  
  Purchase #2 $185.40   7.116%   $198.5931   $198.59   $198.60   $198.60  
  Purchase #3 $166.95   7.764%   $179.912   $179.91   $179.90   $179.90  
  Purchase #4 $68.34   5.312%   $71.9702   $71.97   $71.95   $72.00  
  Purchase #5 $22.39   8.673%   $24.3319   $24.33   $24.35   $24.30  
  Purchase #6 $164.86   9.666%   $180.7954   $180.80   $180.80   $180.80  
  Purchase #7 $223.49   3.480%   $231.2675   $231.27   $231.25   $231.30  
  7 purchase totals = $875.75       $935.3965   $935.40   $935.40   $935.40