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	$72.33	6.818%	$77.2615	$77.26	$77.25	$77.30
Purchase #2	$54.53	8.680%	$59.2632	$59.26	$59.25	$59.30
Purchase #3	$195.59	12.280%	$219.6085	$219.61	$219.60	$219.60
Purchase #4	$98.34	7.205%	$105.4254	$105.43	$105.45	$105.40
Purchase #5	$104.63	10.869%	$116.0022	$116.00	$116.00	$116.00
Purchase #6	$219.60	8.708%	$238.7228	$238.72	$238.70	$238.70
Purchase #7	$151.76	13.392%	$172.0837	$172.08	$172.10	$172.10
7 purchase totals =	$896.78		$988.3673	$988.36	$988.35	$988.40