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	$74.86	7.719%	$80.6384	$80.64	$80.65	$80.60
Purchase #2	$101.25	4.841%	$106.1515	$106.15	$106.15	$106.20
Purchase #3	$250.61	3.281%	$258.8325	$258.83	$258.85	$258.80
Purchase #4	$240.48	9.440%	$263.1813	$263.18	$263.20	$263.20
Purchase #5	$83.61	10.707%	$92.5621	$92.56	$92.55	$92.60
Purchase #6	$95.75	13.739%	$108.9051	$108.91	$108.90	$108.90
Purchase #7	$172.73	7.816%	$186.2306	$186.23	$186.25	$186.20
7 purchase totals =	$1,019.29		$1,096.5015	$1,096.50	$1,096.55	$1,096.50