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	$146.47	12.500%	$164.7788	$164.78	$164.80	$164.80
Purchase #2	$250.91	12.589%	$282.4971	$282.50	$282.50	$282.50
Purchase #3	$190.62	11.131%	$211.8379	$211.84	$211.85	$211.80
Purchase #4	$102.89	6.424%	$109.4997	$109.50	$109.50	$109.50
Purchase #5	$153.84	8.748%	$167.2979	$167.30	$167.30	$167.30
Purchase #6	$204.39	11.598%	$228.0952	$228.10	$228.10	$228.10
Purchase #7	$170.65	8.351%	$184.901	$184.90	$184.90	$184.90
7 purchase totals =	$1,219.77		$1,348.9076	$1,348.92	$1,348.95	$1,348.90