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	$40.29	4.376%	$42.0531	$42.05	$42.05	$42.10
Purchase #2	$185.53	7.323%	$199.1164	$199.12	$199.10	$199.10
Purchase #3	$44.58	6.396%	$47.4313	$47.43	$47.45	$47.40
Purchase #4	$193.98	3.113%	$200.0186	$200.02	$200.00	$200.00
Purchase #5	$134.29	6.753%	$143.3586	$143.36	$143.35	$143.40
Purchase #6	$59.67	3.113%	$61.5275	$61.53	$61.55	$61.50
Purchase #7	$216.98	8.411%	$235.2302	$235.23	$235.25	$235.20
7 purchase totals =	$875.32		$928.7357	$928.74	$928.75	$928.70