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	$131.89	13.324%	$149.463	$149.46	$149.45	$149.50
Purchase #2	$247.27	11.443%	$275.5651	$275.57	$275.55	$275.60
Purchase #3	$121.27	13.294%	$137.3916	$137.39	$137.40	$137.40
Purchase #4	$87.87	5.653%	$92.8373	$92.84	$92.85	$92.80
Purchase #5	$87.89	12.817%	$99.1549	$99.15	$99.15	$99.20
Purchase #6	$230.97	6.771%	$246.609	$246.61	$246.60	$246.60
Purchase #7	$60.33	6.611%	$64.3184	$64.32	$64.30	$64.30
7 purchase totals =	$967.49		$1,065.3393	$1,065.34	$1,065.30	$1,065.40