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	$71.58	3.253%	$73.9085	$73.91	$73.90	$73.90
Purchase #2	$166.90	13.286%	$189.0743	$189.07	$189.05	$189.10
Purchase #3	$19.48	3.615%	$20.1842	$20.18	$20.20	$20.20
Purchase #4	$135.64	13.499%	$153.95	$153.95	$153.95	$154.00
Purchase #5	$166.36	11.668%	$185.7709	$185.77	$185.75	$185.80
Purchase #6	$223.46	12.722%	$251.8886	$251.89	$251.90	$251.90
Purchase #7	$94.44	9.576%	$103.4836	$103.48	$103.50	$103.50
7 purchase totals =	$877.86		$978.2601	$978.25	$978.25	$978.40