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	$111.42	5.438%	$117.479	$117.48	$117.50	$117.50
Purchase #2	$129.77	7.798%	$139.8895	$139.89	$139.90	$139.90
Purchase #3	$27.46	7.788%	$29.5986	$29.60	$29.60	$29.60
Purchase #4	$96.47	3.275%	$99.6294	$99.63	$99.65	$99.60
Purchase #5	$68.28	7.871%	$73.6543	$73.65	$73.65	$73.70
Purchase #6	$103.78	5.425%	$109.4101	$109.41	$109.40	$109.40
Purchase #7	$159.25	12.130%	$178.567	$178.57	$178.55	$178.60
7 purchase totals =	$696.43		$748.2279	$748.23	$748.25	$748.30