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	$125.56	4.370%	$131.047	$131.05	$131.05	$131.00
Purchase #2	$199.52	11.757%	$222.9776	$222.98	$223.00	$223.00
Purchase #3	$89.77	10.709%	$99.3835	$99.38	$99.40	$99.40
Purchase #4	$25.62	12.529%	$28.8299	$28.83	$28.85	$28.80
Purchase #5	$114.58	10.696%	$126.8355	$126.84	$126.85	$126.80
Purchase #6	$43.95	11.817%	$49.1436	$49.14	$49.15	$49.10
Purchase #7	$35.52	13.518%	$40.3216	$40.32	$40.30	$40.30
7 purchase totals =	$634.52		$698.5387	$698.54	$698.60	$698.40