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	$237.83	7.152%	$254.8396	$254.84	$254.85	$254.80
Purchase #2	$101.48	6.610%	$108.1878	$108.19	$108.20	$108.20
Purchase #3	$6.87	11.321%	$7.6478	$7.65	$7.65	$7.60
Purchase #4	$42.41	7.337%	$45.5216	$45.52	$45.50	$45.50
Purchase #5	$64.40	4.109%	$67.0462	$67.05	$67.05	$67.00
Purchase #6	$182.57	11.809%	$204.1297	$204.13	$204.15	$204.10
Purchase #7	$148.33	13.729%	$168.6942	$168.69	$168.70	$168.70
7 purchase totals =	$783.89		$856.0669	$856.07	$856.10	$855.90