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	$66.64	12.433%	$74.9254	$74.93	$74.95	$74.90
Purchase #2	$47.79	6.127%	$50.7181	$50.72	$50.70	$50.70
Purchase #3	$89.31	12.795%	$100.7372	$100.74	$100.75	$100.70
Purchase #4	$207.99	7.440%	$223.4645	$223.46	$223.45	$223.50
Purchase #5	$52.43	5.334%	$55.2266	$55.23	$55.25	$55.20
Purchase #6	$213.77	7.256%	$229.2812	$229.28	$229.30	$229.30
Purchase #7	$226.45	7.605%	$243.6715	$243.67	$243.65	$243.70
7 purchase totals =	$904.38		$978.0245	$978.03	$978.05	$978.00