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	$228.70	9.242%	$249.8365	$249.84	$249.85	$249.80
Purchase #2	$122.88	3.505%	$127.1869	$127.19	$127.20	$127.20
Purchase #3	$100.77	8.803%	$109.6408	$109.64	$109.65	$109.60
Purchase #4	$136.51	6.179%	$144.945	$144.95	$144.95	$144.90
Purchase #5	$175.72	8.254%	$190.2239	$190.22	$190.20	$190.20
Purchase #6	$136.80	7.843%	$147.5292	$147.53	$147.55	$147.50
Purchase #7	$224.31	8.405%	$243.1633	$243.16	$243.15	$243.20
7 purchase totals =	$1,125.69		$1,212.5256	$1,212.53	$1,212.55	$1,212.40