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	$71.36	11.840%	$79.809	$79.81	$79.80	$79.80
Purchase #2	$178.90	7.595%	$192.4875	$192.49	$192.50	$192.50
Purchase #3	$35.91	12.662%	$40.4569	$40.46	$40.45	$40.50
Purchase #4	$104.25	7.104%	$111.6559	$111.66	$111.65	$111.70
Purchase #5	$34.25	9.556%	$37.5229	$37.52	$37.50	$37.50
Purchase #6	$79.86	13.108%	$90.328	$90.33	$90.35	$90.30
Purchase #7	$85.61	13.128%	$96.8489	$96.85	$96.85	$96.80
7 purchase totals =	$590.14		$649.1091	$649.12	$649.10	$649.10