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	$238.95	11.314%	$265.9848	$265.98	$266.00	$266.00
Purchase #2	$34.96	8.228%	$37.8365	$37.84	$37.85	$37.80
Purchase #3	$88.31	4.363%	$92.163	$92.16	$92.15	$92.20
Purchase #4	$42.35	6.307%	$45.021	$45.02	$45.00	$45.00
Purchase #5	$143.45	9.564%	$157.1696	$157.17	$157.15	$157.20
Purchase #6	$212.95	12.369%	$239.2898	$239.29	$239.30	$239.30
Purchase #7	$85.41	4.307%	$89.0886	$89.09	$89.10	$89.10
7 purchase totals =	$846.38		$926.5533	$926.55	$926.55	$926.60