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	$122.86	7.623%	$132.2256	$132.23	$132.25	$132.20
Purchase #2	$91.44	9.204%	$99.8561	$99.86	$99.85	$99.90
Purchase #3	$213.77	7.337%	$229.4543	$229.45	$229.45	$229.50
Purchase #4	$77.91	6.679%	$83.1136	$83.11	$83.10	$83.10
Purchase #5	$152.33	7.821%	$164.2437	$164.24	$164.25	$164.20
Purchase #6	$25.83	6.481%	$27.504	$27.50	$27.50	$27.50
Purchase #7	$54.70	11.746%	$61.1251	$61.13	$61.15	$61.10
7 purchase totals =	$738.84		$797.5224	$797.52	$797.55	$797.50