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 $213.72   12.282%   $239.9691   $239.97   $239.95   $240.00  
  Purchase #2 $60.37   9.265%   $65.9633   $65.96   $65.95   $66.00  
  Purchase #3 $19.86   12.841%   $22.4102   $22.41   $22.40   $22.40  
  Purchase #4 $208.51   11.439%   $232.3615   $232.36   $232.35   $232.40  
  Purchase #5 $189.62   9.608%   $207.8387   $207.84   $207.85   $207.80  
  Purchase #6 $174.98   12.123%   $196.1928   $196.19   $196.20   $196.20  
  Purchase #7 $195.76   11.627%   $218.521   $218.52   $218.50   $218.50  
  7 purchase totals = $1,062.82       $1,183.2566   $1,183.25   $1,183.20   $1,183.30