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	$188.78	3.421%	$195.2382	$195.24	$195.25	$195.20
Purchase #2	$7.71	9.727%	$8.46	$8.46	$8.45	$8.50
Purchase #3	$18.93	6.812%	$20.2195	$20.22	$20.20	$20.20
Purchase #4	$63.31	3.841%	$65.7417	$65.74	$65.75	$65.70
Purchase #5	$90.95	9.759%	$99.8258	$99.83	$99.85	$99.80
Purchase #6	$208.96	4.145%	$217.6214	$217.62	$217.60	$217.60
Purchase #7	$222.90	11.456%	$248.4354	$248.44	$248.45	$248.40
7 purchase totals =	$801.54		$855.5420	$855.55	$855.55	$855.40