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	$19.50	5.312%	$20.5358	$20.54	$20.55	$20.50
Purchase #2	$127.25	9.323%	$139.1135	$139.11	$139.10	$139.10
Purchase #3	$33.57	7.654%	$36.1394	$36.14	$36.15	$36.10
Purchase #4	$30.84	13.749%	$35.0802	$35.08	$35.10	$35.10
Purchase #5	$79.33	12.655%	$89.3692	$89.37	$89.35	$89.40
Purchase #6	$242.47	11.129%	$269.4545	$269.45	$269.45	$269.50
Purchase #7	$32.59	11.487%	$36.3336	$36.33	$36.35	$36.30
7 purchase totals =	$565.55		$626.0262	$626.02	$626.05	$626.00