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 $160.79   10.466%   $177.6183   $177.62   $177.60   $177.60  
  Purchase #2 $54.66   11.596%   $60.9984   $61.00   $61.00   $61.00  
  Purchase #3 $11.30   9.441%   $12.3668   $12.37   $12.35   $12.40  
  Purchase #4 $69.85   8.625%   $75.8746   $75.87   $75.85   $75.90  
  Purchase #5 $221.84   5.302%   $233.602   $233.60   $233.60   $233.60  
  Purchase #6 $112.34   9.355%   $122.8494   $122.85   $122.85   $122.80  
  Purchase #7 $27.96   7.262%   $29.9905   $29.99   $30.00   $30.00  
  7 purchase totals = $658.74       $713.3000   $713.30   $713.25   $713.30