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 $119.86   12.261%   $134.556   $134.56   $134.55   $134.60  
  Purchase #2 $54.30   7.838%   $58.556   $58.56   $58.55   $58.60  
  Purchase #3 $179.99   3.565%   $186.4066   $186.41   $186.40   $186.40  
  Purchase #4 $58.82   10.443%   $64.9626   $64.96   $64.95   $65.00  
  Purchase #5 $19.55   3.177%   $20.1711   $20.17   $20.15   $20.20  
  Purchase #6 $48.33   13.378%   $54.7956   $54.80   $54.80   $54.80  
  Purchase #7 $41.86   3.341%   $43.2585   $43.26   $43.25   $43.30  
  7 purchase totals = $522.71       $562.7064   $562.72   $562.65   $562.90