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	$64.83	3.830%	$67.313	$67.31	$67.30	$67.30
Purchase #2	$15.77	11.719%	$17.6181	$17.62	$17.60	$17.60
Purchase #3	$55.68	3.140%	$57.4284	$57.43	$57.45	$57.40
Purchase #4	$250.35	10.378%	$276.3313	$276.33	$276.35	$276.30
Purchase #5	$98.73	10.599%	$109.1944	$109.19	$109.20	$109.20
Purchase #6	$74.93	7.301%	$80.4006	$80.40	$80.40	$80.40
Purchase #7	$42.89	6.853%	$45.8293	$45.83	$45.85	$45.80
7 purchase totals =	$603.18		$654.1151	$654.11	$654.15	$654.00