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	$80.79	5.351%	$85.1131	$85.11	$85.10	$85.10
Purchase #2	$165.38	12.143%	$185.4621	$185.46	$185.45	$185.50
Purchase #3	$54.91	8.532%	$59.5949	$59.59	$59.60	$59.60
Purchase #4	$127.81	10.375%	$141.0703	$141.07	$141.05	$141.10
Purchase #5	$203.36	13.218%	$230.2401	$230.24	$230.25	$230.20
Purchase #6	$182.62	4.810%	$191.404	$191.40	$191.40	$191.40
Purchase #7	$220.48	7.246%	$236.456	$236.46	$236.45	$236.50
7 purchase totals =	$1,035.35		$1,129.3405	$1,129.33	$1,129.30	$1,129.40