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	$189.32	12.354%	$212.7086	$212.71	$212.70	$212.70
Purchase #2	$19.51	12.328%	$21.9152	$21.92	$21.90	$21.90
Purchase #3	$62.31	6.615%	$66.4318	$66.43	$66.45	$66.40
Purchase #4	$125.95	13.224%	$142.6056	$142.61	$142.60	$142.60
Purchase #5	$82.98	6.139%	$88.0741	$88.07	$88.05	$88.10
Purchase #6	$146.93	10.804%	$162.8043	$162.80	$162.80	$162.80
Purchase #7	$32.29	4.632%	$33.7857	$33.79	$33.80	$33.80
7 purchase totals =	$659.29		$728.3253	$728.33	$728.30	$728.30