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	$9.29	11.483%	$10.3568	$10.36	$10.35	$10.40
Purchase #2	$73.84	9.375%	$80.7625	$80.76	$80.75	$80.80
Purchase #3	$226.84	6.159%	$240.8111	$240.81	$240.80	$240.80
Purchase #4	$70.66	10.501%	$78.08	$78.08	$78.10	$78.10
Purchase #5	$211.89	4.623%	$221.6857	$221.69	$221.70	$221.70
Purchase #6	$89.62	10.131%	$98.6994	$98.70	$98.70	$98.70
Purchase #7	$83.76	6.627%	$89.3108	$89.31	$89.30	$89.30
7 purchase totals =	$765.90		$819.7063	$819.71	$819.70	$819.80