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 $146.47   9.262%   $160.0361   $160.04   $160.05   $160.00  
  Purchase #2 $185.89   6.817%   $198.5621   $198.56   $198.55   $198.60  
  Purchase #3 $232.67   6.103%   $246.8699   $246.87   $246.85   $246.90  
  Purchase #4 $237.58   5.775%   $251.3002   $251.30   $251.30   $251.30  
  Purchase #5 $86.97   13.827%   $98.9953   $99.00   $99.00   $99.00  
  Purchase #6 $232.57   11.426%   $259.1434   $259.14   $259.15   $259.10  
  Purchase #7 $42.58   12.798%   $48.0294   $48.03   $48.05   $48.00  
  7 purchase totals = $1,164.73       $1,262.9364   $1,262.94   $1,262.95   $1,262.90