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	$148.59	13.210%	$168.2187	$168.22	$168.20	$168.20
Purchase #2	$169.63	8.238%	$183.6041	$183.60	$183.60	$183.60
Purchase #3	$230.34	10.520%	$254.5718	$254.57	$254.55	$254.60
Purchase #4	$49.84	7.317%	$53.4868	$53.49	$53.50	$53.50
Purchase #5	$152.45	11.115%	$169.3948	$169.39	$169.40	$169.40
Purchase #6	$165.90	11.510%	$184.9951	$185.00	$185.00	$185.00
Purchase #7	$250.66	11.657%	$279.8794	$279.88	$279.90	$279.90
7 purchase totals =	$1,167.41		$1,294.1507	$1,294.15	$1,294.15	$1,294.20