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	$20.62	12.583%	$23.2146	$23.21	$23.20	$23.20
Purchase #2	$75.44	6.829%	$80.5918	$80.59	$80.60	$80.60
Purchase #3	$145.57	4.548%	$152.1905	$152.19	$152.20	$152.20
Purchase #4	$167.70	10.349%	$185.0553	$185.06	$185.05	$185.10
Purchase #5	$108.83	9.573%	$119.2483	$119.25	$119.25	$119.20
Purchase #6	$156.71	7.614%	$168.6419	$168.64	$168.65	$168.60
Purchase #7	$179.89	9.294%	$196.609	$196.61	$196.60	$196.60
7 purchase totals =	$854.76		$925.5514	$925.55	$925.55	$925.50