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 $76.34   8.202%   $82.6014   $82.60   $82.60   $82.60  
  Purchase #2 $85.25   12.607%   $95.9975   $96.00   $96.00   $96.00  
  Purchase #3 $26.86   13.624%   $30.5194   $30.52   $30.50   $30.50  
  Purchase #4 $137.40   5.779%   $145.3403   $145.34   $145.35   $145.30  
  Purchase #5 $186.46   10.298%   $205.6617   $205.66   $205.65   $205.70  
  Purchase #6 $186.55   12.261%   $209.4229   $209.42   $209.40   $209.40  
  Purchase #7 $10.26   6.829%   $10.9607   $10.96   $10.95   $11.00  
  7 purchase totals = $709.12       $780.5039   $780.50   $780.45   $780.50