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	$138.73	10.493%	$153.2869	$153.29	$153.30	$153.30
Purchase #2	$131.59	6.304%	$139.8854	$139.89	$139.90	$139.90
Purchase #3	$55.64	10.751%	$61.6219	$61.62	$61.60	$61.60
Purchase #4	$109.88	13.820%	$125.0654	$125.07	$125.05	$125.10
Purchase #5	$237.92	4.437%	$248.4765	$248.48	$248.50	$248.50
Purchase #6	$105.58	3.442%	$109.2141	$109.21	$109.20	$109.20
Purchase #7	$249.45	12.379%	$280.3294	$280.33	$280.35	$280.30
7 purchase totals =	$1,028.79		$1,117.8796	$1,117.89	$1,117.90	$1,117.90