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	$71.81	10.184%	$79.1231	$79.12	$79.10	$79.10
Purchase #2	$244.86	3.456%	$253.3224	$253.32	$253.30	$253.30
Purchase #3	$33.66	8.143%	$36.4009	$36.40	$36.40	$36.40
Purchase #4	$226.30	9.418%	$247.6129	$247.61	$247.60	$247.60
Purchase #5	$87.45	13.512%	$99.2662	$99.27	$99.25	$99.30
Purchase #6	$201.61	9.234%	$220.2267	$220.23	$220.25	$220.20
Purchase #7	$154.51	6.384%	$164.3739	$164.37	$164.35	$164.40
7 purchase totals =	$1,020.20		$1,100.3261	$1,100.32	$1,100.25	$1,100.30