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	$54.77	8.241%	$59.2836	$59.28	$59.30	$59.30
Purchase #2	$45.25	10.521%	$50.0108	$50.01	$50.00	$50.00
Purchase #3	$74.90	7.728%	$80.6883	$80.69	$80.70	$80.70
Purchase #4	$48.85	9.147%	$53.3183	$53.32	$53.30	$53.30
Purchase #5	$140.59	7.148%	$150.6394	$150.64	$150.65	$150.60
Purchase #6	$242.99	4.348%	$253.5552	$253.56	$253.55	$253.60
Purchase #7	$229.55	6.585%	$244.6659	$244.67	$244.65	$244.70
7 purchase totals =	$836.90		$892.1615	$892.17	$892.15	$892.20