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	$48.29	11.667%	$53.924	$53.92	$53.90	$53.90
Purchase #2	$13.57	6.854%	$14.5001	$14.50	$14.50	$14.50
Purchase #3	$72.26	11.580%	$80.6277	$80.63	$80.65	$80.60
Purchase #4	$195.33	13.564%	$221.8246	$221.82	$221.80	$221.80
Purchase #5	$85.46	4.868%	$89.6202	$89.62	$89.60	$89.60
Purchase #6	$205.69	12.536%	$231.4753	$231.48	$231.50	$231.50
Purchase #7	$53.25	9.476%	$58.296	$58.30	$58.30	$58.30
7 purchase totals =	$673.85		$750.2679	$750.27	$750.25	$750.20