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	$29.39	12.192%	$32.9732	$32.97	$32.95	$33.00
Purchase #2	$77.30	7.720%	$83.2676	$83.27	$83.25	$83.30
Purchase #3	$27.76	12.804%	$31.3144	$31.31	$31.30	$31.30
Purchase #4	$11.61	3.325%	$11.996	$12.00	$12.00	$12.00
Purchase #5	$243.46	12.132%	$272.9966	$273.00	$273.00	$273.00
Purchase #6	$92.77	7.227%	$99.4745	$99.47	$99.45	$99.50
Purchase #7	$74.61	10.415%	$82.3806	$82.38	$82.40	$82.40
7 purchase totals =	$556.90		$614.4029	$614.40	$614.35	$614.50