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	$90.65	12.685%	$102.149	$102.15	$102.15	$102.10
Purchase #2	$100.79	12.226%	$113.1126	$113.11	$113.10	$113.10
Purchase #3	$236.26	13.408%	$267.9377	$267.94	$267.95	$267.90
Purchase #4	$94.39	5.572%	$99.6494	$99.65	$99.65	$99.60
Purchase #5	$222.32	3.362%	$229.7944	$229.79	$229.80	$229.80
Purchase #6	$146.95	12.741%	$165.6729	$165.67	$165.65	$165.70
Purchase #7	$89.92	7.440%	$96.61	$96.61	$96.60	$96.60
7 purchase totals =	$981.28		$1,074.9260	$1,074.92	$1,074.90	$1,074.80