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	$192.61	13.392%	$218.4043	$218.40	$218.40	$218.40
Purchase #2	$54.95	3.659%	$56.9606	$56.96	$56.95	$57.00
Purchase #3	$54.36	12.790%	$61.3126	$61.31	$61.30	$61.30
Purchase #4	$241.81	3.287%	$249.7583	$249.76	$249.75	$249.80
Purchase #5	$36.52	3.239%	$37.7029	$37.70	$37.70	$37.70
Purchase #6	$235.90	6.195%	$250.514	$250.51	$250.50	$250.50
Purchase #7	$99.91	11.787%	$111.6864	$111.69	$111.70	$111.70
7 purchase totals =	$916.06		$986.3391	$986.33	$986.30	$986.40