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	$130.76	8.328%	$141.6497	$141.65	$141.65	$141.60
Purchase #2	$41.76	3.861%	$43.3724	$43.37	$43.35	$43.40
Purchase #3	$124.69	12.200%	$139.9022	$139.90	$139.90	$139.90
Purchase #4	$203.52	8.730%	$221.2873	$221.29	$221.30	$221.30
Purchase #5	$127.76	10.521%	$141.2016	$141.20	$141.20	$141.20
Purchase #6	$40.40	3.102%	$41.6532	$41.65	$41.65	$41.70
Purchase #7	$51.41	4.784%	$53.8695	$53.87	$53.85	$53.90
7 purchase totals =	$720.30		$782.9359	$782.93	$782.90	$783.00