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	$110.60	12.816%	$124.7745	$124.77	$124.75	$124.80
Purchase #2	$46.40	3.490%	$48.0194	$48.02	$48.00	$48.00
Purchase #3	$60.96	12.612%	$68.6483	$68.65	$68.65	$68.60
Purchase #4	$221.78	3.106%	$228.6685	$228.67	$228.65	$228.70
Purchase #5	$99.32	12.251%	$111.4877	$111.49	$111.50	$111.50
Purchase #6	$50.87	9.280%	$55.5907	$55.59	$55.60	$55.60
Purchase #7	$25.54	10.221%	$28.1504	$28.15	$28.15	$28.20
7 purchase totals =	$615.47		$665.3395	$665.34	$665.30	$665.40