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	$182.27	12.288%	$204.6673	$204.67	$204.65	$204.70
Purchase #2	$128.45	4.427%	$134.1365	$134.14	$134.15	$134.10
Purchase #3	$123.66	5.735%	$130.7519	$130.75	$130.75	$130.80
Purchase #4	$80.71	12.526%	$90.8197	$90.82	$90.80	$90.80
Purchase #5	$74.77	12.212%	$83.9009	$83.90	$83.90	$83.90
Purchase #6	$36.25	10.655%	$40.1124	$40.11	$40.10	$40.10
Purchase #7	$157.58	8.648%	$171.2075	$171.21	$171.20	$171.20
7 purchase totals =	$783.69		$855.5962	$855.60	$855.55	$855.60