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	$130.59	11.198%	$145.2135	$145.21	$145.20	$145.20
Purchase #2	$82.39	8.811%	$89.6494	$89.65	$89.65	$89.60
Purchase #3	$53.33	4.777%	$55.8776	$55.88	$55.90	$55.90
Purchase #4	$143.91	11.600%	$160.6036	$160.60	$160.60	$160.60
Purchase #5	$225.66	6.372%	$240.0391	$240.04	$240.05	$240.00
Purchase #6	$137.95	4.543%	$144.2171	$144.22	$144.20	$144.20
Purchase #7	$117.34	12.256%	$131.7212	$131.72	$131.70	$131.70
7 purchase totals =	$891.17		$967.3215	$967.32	$967.30	$967.20