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	$7.52	10.586%	$8.3161	$8.32	$8.30	$8.30
Purchase #2	$144.28	6.264%	$153.3177	$153.32	$153.30	$153.30
Purchase #3	$159.29	7.102%	$170.6028	$170.60	$170.60	$170.60
Purchase #4	$97.54	8.597%	$105.9255	$105.93	$105.95	$105.90
Purchase #5	$166.57	3.171%	$171.8519	$171.85	$171.85	$171.90
Purchase #6	$60.85	10.590%	$67.294	$67.29	$67.30	$67.30
Purchase #7	$51.54	9.852%	$56.6177	$56.62	$56.60	$56.60
7 purchase totals =	$687.59		$733.9257	$733.93	$733.90	$733.90