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 $134.37   5.564%   $141.8463   $141.85   $141.85   $141.80  
  Purchase #2 $163.63   10.401%   $180.6492   $180.65   $180.65   $180.60  
  Purchase #3 $84.72   13.275%   $95.9666   $95.97   $95.95   $96.00  
  Purchase #4 $78.41   9.715%   $86.0275   $86.03   $86.05   $86.00  
  Purchase #5 $215.95   11.721%   $241.2615   $241.26   $241.25   $241.30  
  Purchase #6 $127.39   12.799%   $143.6946   $143.69   $143.70   $143.70  
  Purchase #7 $107.52   7.428%   $115.5066   $115.51   $115.50   $115.50  
  7 purchase totals = $911.99       $1,004.9523   $1,004.96   $1,004.95   $1,004.90