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	$88.45	12.463%	$99.4735	$99.47	$99.45	$99.50
Purchase #2	$246.44	5.749%	$260.6078	$260.61	$260.60	$260.60
Purchase #3	$235.39	12.519%	$264.8585	$264.86	$264.85	$264.90
Purchase #4	$49.72	7.389%	$53.3938	$53.39	$53.40	$53.40
Purchase #5	$84.80	7.674%	$91.3076	$91.31	$91.30	$91.30
Purchase #6	$85.63	5.184%	$90.0691	$90.07	$90.05	$90.10
Purchase #7	$54.49	3.740%	$56.5279	$56.53	$56.55	$56.50
7 purchase totals =	$844.92		$916.2382	$916.24	$916.20	$916.30