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	$74.84	4.452%	$78.1719	$78.17	$78.15	$78.20
Purchase #2	$139.48	10.138%	$153.6205	$153.62	$153.60	$153.60
Purchase #3	$166.72	10.302%	$183.8955	$183.90	$183.90	$183.90
Purchase #4	$76.77	11.155%	$85.3337	$85.33	$85.35	$85.30
Purchase #5	$63.30	5.512%	$66.7891	$66.79	$66.80	$66.80
Purchase #6	$135.88	8.410%	$147.3075	$147.31	$147.30	$147.30
Purchase #7	$12.52	12.236%	$14.0519	$14.05	$14.05	$14.10
7 purchase totals =	$669.51		$729.1701	$729.17	$729.15	$729.20