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	$99.91	6.821%	$106.7249	$106.72	$106.70	$106.70
Purchase #2	$92.35	8.280%	$99.9966	$100.00	$100.00	$100.00
Purchase #3	$181.37	8.157%	$196.1644	$196.16	$196.15	$196.20
Purchase #4	$113.46	12.597%	$127.7526	$127.75	$127.75	$127.80
Purchase #5	$135.93	12.642%	$153.1143	$153.11	$153.10	$153.10
Purchase #6	$81.98	12.716%	$92.4046	$92.40	$92.40	$92.40
Purchase #7	$55.76	8.454%	$60.474	$60.47	$60.45	$60.50
7 purchase totals =	$760.76		$836.6314	$836.61	$836.55	$836.70