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	$81.71	11.635%	$91.217	$91.22	$91.20	$91.20
Purchase #2	$147.40	12.276%	$165.4948	$165.49	$165.50	$165.50
Purchase #3	$159.56	4.868%	$167.3274	$167.33	$167.35	$167.30
Purchase #4	$175.41	5.103%	$184.3612	$184.36	$184.35	$184.40
Purchase #5	$181.60	10.220%	$200.1595	$200.16	$200.15	$200.20
Purchase #6	$206.50	10.482%	$228.1453	$228.15	$228.15	$228.10
Purchase #7	$84.86	5.651%	$89.6554	$89.66	$89.65	$89.70
7 purchase totals =	$1,037.04		$1,126.3606	$1,126.37	$1,126.35	$1,126.40