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 $61.42   7.407%   $65.9694   $65.97   $65.95   $66.00  
  Purchase #2 $245.55   3.290%   $253.6286   $253.63   $253.65   $253.60  
  Purchase #3 $121.47   7.719%   $130.8463   $130.85   $130.85   $130.80  
  Purchase #4 $240.79   7.724%   $259.3886   $259.39   $259.40   $259.40  
  Purchase #5 $191.42   9.340%   $209.2986   $209.30   $209.30   $209.30  
  Purchase #6 $219.98   13.192%   $248.9998   $249.00   $249.00   $249.00  
  Purchase #7 $148.45   5.439%   $156.5242   $156.52   $156.50   $156.50  
  7 purchase totals = $1,229.08       $1,324.6555   $1,324.66   $1,324.65   $1,324.60