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	$198.77	13.756%	$226.1128	$226.11	$226.10	$226.10
Purchase #2	$64.68	9.656%	$70.9255	$70.93	$70.95	$70.90
Purchase #3	$249.80	12.117%	$280.0683	$280.07	$280.05	$280.10
Purchase #4	$229.92	8.735%	$250.0035	$250.00	$250.00	$250.00
Purchase #5	$105.29	6.287%	$111.9096	$111.91	$111.90	$111.90
Purchase #6	$215.37	3.467%	$222.8369	$222.84	$222.85	$222.80
Purchase #7	$230.59	10.391%	$254.5506	$254.55	$254.55	$254.60
7 purchase totals =	$1,294.42		$1,416.4072	$1,416.41	$1,416.40	$1,416.40