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	$147.86	12.142%	$165.8132	$165.81	$165.80	$165.80
Purchase #2	$82.31	9.755%	$90.3393	$90.34	$90.35	$90.30
Purchase #3	$78.47	6.312%	$83.423	$83.42	$83.40	$83.40
Purchase #4	$228.52	13.652%	$259.7176	$259.72	$259.70	$259.70
Purchase #5	$130.77	3.176%	$134.9233	$134.92	$134.90	$134.90
Purchase #6	$129.82	10.580%	$143.555	$143.56	$143.55	$143.60
Purchase #7	$61.93	3.679%	$64.2084	$64.21	$64.20	$64.20
7 purchase totals =	$859.68		$941.9798	$941.98	$941.90	$941.90