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	$174.78	4.414%	$182.4948	$182.49	$182.50	$182.50
Purchase #2	$184.30	7.604%	$198.3142	$198.31	$198.30	$198.30
Purchase #3	$80.80	12.746%	$91.0988	$91.10	$91.10	$91.10
Purchase #4	$149.56	12.165%	$167.754	$167.75	$167.75	$167.80
Purchase #5	$102.97	8.205%	$111.4187	$111.42	$111.40	$111.40
Purchase #6	$238.33	13.300%	$270.0279	$270.03	$270.05	$270.00
Purchase #7	$96.28	4.171%	$100.2958	$100.30	$100.30	$100.30
7 purchase totals =	$1,027.02		$1,121.4042	$1,121.40	$1,121.40	$1,121.40