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 $54.30   7.865%   $58.5707   $58.57   $58.55   $58.60  
  Purchase #2 $169.69   5.617%   $179.2215   $179.22   $179.20   $179.20  
  Purchase #3 $107.26   13.629%   $121.8785   $121.88   $121.90   $121.90  
  Purchase #4 $40.82   13.546%   $46.3495   $46.35   $46.35   $46.30  
  Purchase #5 $177.55   12.113%   $199.0566   $199.06   $199.05   $199.10  
  Purchase #6 $205.82   6.829%   $219.8754   $219.88   $219.90   $219.90  
  Purchase #7 $228.86   9.851%   $251.405   $251.41   $251.40   $251.40  
  7 purchase totals = $984.30       $1,076.3572   $1,076.37   $1,076.35   $1,076.40