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	$92.50	7.365%	$99.3126	$99.31	$99.30	$99.30
Purchase #2	$37.76	12.305%	$42.4064	$42.41	$42.40	$42.40
Purchase #3	$135.53	6.767%	$144.7013	$144.70	$144.70	$144.70
Purchase #4	$226.30	12.259%	$254.0421	$254.04	$254.05	$254.00
Purchase #5	$92.61	11.642%	$103.3917	$103.39	$103.40	$103.40
Purchase #6	$86.72	13.131%	$98.1072	$98.11	$98.10	$98.10
Purchase #7	$142.56	3.252%	$147.1961	$147.20	$147.20	$147.20
7 purchase totals =	$813.98		$889.1574	$889.16	$889.15	$889.10