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	$172.92	7.405%	$185.7247	$185.72	$185.70	$185.70
Purchase #2	$145.81	10.297%	$160.8241	$160.82	$160.80	$160.80
Purchase #3	$144.33	3.437%	$149.2906	$149.29	$149.30	$149.30
Purchase #4	$158.31	7.310%	$169.8825	$169.88	$169.90	$169.90
Purchase #5	$67.59	12.119%	$75.7812	$75.78	$75.80	$75.80
Purchase #6	$17.50	13.663%	$19.891	$19.89	$19.90	$19.90
Purchase #7	$57.52	12.278%	$64.5823	$64.58	$64.60	$64.60
7 purchase totals =	$763.98		$825.9764	$825.96	$826.00	$826.00