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	$30.94	9.237%	$33.7979	$33.80	$33.80	$33.80
Purchase #2	$240.86	13.180%	$272.6053	$272.61	$272.60	$272.60
Purchase #3	$233.35	9.424%	$255.3409	$255.34	$255.35	$255.30
Purchase #4	$88.65	3.278%	$91.5559	$91.56	$91.55	$91.60
Purchase #5	$216.96	5.605%	$229.1206	$229.12	$229.10	$229.10
Purchase #6	$141.31	12.601%	$159.1165	$159.12	$159.10	$159.10
Purchase #7	$118.53	7.437%	$127.3451	$127.35	$127.35	$127.30
7 purchase totals =	$1,070.60		$1,168.8822	$1,168.90	$1,168.85	$1,168.80