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	$80.50	11.260%	$89.5643	$89.56	$89.55	$89.60
Purchase #2	$79.87	13.752%	$90.8537	$90.85	$90.85	$90.90
Purchase #3	$134.79	3.285%	$139.2179	$139.22	$139.20	$139.20
Purchase #4	$32.92	6.399%	$35.0266	$35.03	$35.05	$35.00
Purchase #5	$58.32	5.215%	$61.3614	$61.36	$61.35	$61.40
Purchase #6	$233.32	3.477%	$241.4325	$241.43	$241.45	$241.40
Purchase #7	$200.91	12.571%	$226.1664	$226.17	$226.15	$226.20
7 purchase totals =	$820.63		$883.6228	$883.62	$883.60	$883.70