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 $186.32   4.250%   $194.2386   $194.24   $194.25   $194.20  
  Purchase #2 $43.66   6.802%   $46.6298   $46.63   $46.65   $46.60  
  Purchase #3 $71.41   3.628%   $74.0008   $74.00   $74.00   $74.00  
  Purchase #4 $70.56   3.254%   $72.856   $72.86   $72.85   $72.90  
  Purchase #5 $149.31   7.454%   $160.4396   $160.44   $160.45   $160.40  
  Purchase #6 $147.87   8.721%   $160.7657   $160.77   $160.75   $160.80  
  Purchase #7 $80.86   6.416%   $86.048   $86.05   $86.05   $86.00  
  7 purchase totals = $749.99       $794.9785   $794.99   $795.00   $794.90