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	$52.64	5.411%	$55.4884	$55.49	$55.50	$55.50
Purchase #2	$73.34	7.466%	$78.8156	$78.82	$78.80	$78.80
Purchase #3	$95.62	5.554%	$100.9307	$100.93	$100.95	$100.90
Purchase #4	$248.46	11.864%	$277.9373	$277.94	$277.95	$277.90
Purchase #5	$181.43	10.147%	$199.8397	$199.84	$199.85	$199.80
Purchase #6	$219.54	5.307%	$231.191	$231.19	$231.20	$231.20
Purchase #7	$28.45	6.453%	$30.2859	$30.29	$30.30	$30.30
7 purchase totals =	$899.48		$974.4886	$974.50	$974.55	$974.40