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	$99.86	5.274%	$105.1266	$105.13	$105.15	$105.10
Purchase #2	$99.60	6.292%	$105.8668	$105.87	$105.85	$105.90
Purchase #3	$136.48	4.417%	$142.5083	$142.51	$142.50	$142.50
Purchase #4	$228.90	10.708%	$253.4106	$253.41	$253.40	$253.40
Purchase #5	$235.71	8.110%	$254.8261	$254.83	$254.85	$254.80
Purchase #6	$127.34	3.382%	$131.6466	$131.65	$131.65	$131.60
Purchase #7	$71.77	12.545%	$80.7735	$80.77	$80.75	$80.80
7 purchase totals =	$999.66		$1,074.1585	$1,074.17	$1,074.15	$1,074.10