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	$17.99	9.631%	$19.7226	$19.72	$19.70	$19.70
Purchase #2	$46.46	6.760%	$49.6007	$49.60	$49.60	$49.60
Purchase #3	$83.69	3.711%	$86.7957	$86.80	$86.80	$86.80
Purchase #4	$233.38	9.409%	$255.3387	$255.34	$255.35	$255.30
Purchase #5	$154.72	6.112%	$164.1765	$164.18	$164.20	$164.20
Purchase #6	$213.31	11.647%	$238.1542	$238.15	$238.15	$238.20
Purchase #7	$9.31	11.805%	$10.409	$10.41	$10.40	$10.40
7 purchase totals =	$758.86		$824.1974	$824.20	$824.20	$824.20