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	$43.35	4.570%	$45.3311	$45.33	$45.35	$45.30
Purchase #2	$35.65	12.557%	$40.1266	$40.13	$40.15	$40.10
Purchase #3	$97.82	8.648%	$106.2795	$106.28	$106.30	$106.30
Purchase #4	$120.51	11.450%	$134.3084	$134.31	$134.30	$134.30
Purchase #5	$9.80	7.402%	$10.5254	$10.53	$10.55	$10.50
Purchase #6	$208.61	5.156%	$219.3659	$219.37	$219.35	$219.40
Purchase #7	$102.27	8.587%	$111.0519	$111.05	$111.05	$111.10
7 purchase totals =	$618.01		$666.9888	$667.00	$667.05	$667.00