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	$5.52	4.625%	$5.7753	$5.78	$5.80	$5.80
Purchase #2	$11.86	3.174%	$12.2364	$12.24	$12.25	$12.20
Purchase #3	$237.89	12.323%	$267.2052	$267.21	$267.20	$267.20
Purchase #4	$116.98	12.745%	$131.8891	$131.89	$131.90	$131.90
Purchase #5	$234.45	6.815%	$250.4278	$250.43	$250.45	$250.40
Purchase #6	$250.33	8.518%	$271.6531	$271.65	$271.65	$271.70
Purchase #7	$88.81	11.745%	$99.2407	$99.24	$99.25	$99.20
7 purchase totals =	$945.84		$1,038.4276	$1,038.44	$1,038.50	$1,038.40