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	$55.76	3.290%	$57.5945	$57.59	$57.60	$57.60
Purchase #2	$65.37	5.675%	$69.0797	$69.08	$69.10	$69.10
Purchase #3	$29.29	12.511%	$32.9545	$32.95	$32.95	$33.00
Purchase #4	$229.67	10.705%	$254.2562	$254.26	$254.25	$254.30
Purchase #5	$181.45	10.427%	$200.3698	$200.37	$200.35	$200.40
Purchase #6	$50.48	10.716%	$55.8894	$55.89	$55.90	$55.90
Purchase #7	$99.71	4.689%	$104.3854	$104.39	$104.40	$104.40
7 purchase totals =	$711.73		$774.5295	$774.53	$774.55	$774.70