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	$82.85	8.345%	$89.7638	$89.76	$89.75	$89.80
Purchase #2	$154.93	7.787%	$166.9944	$166.99	$167.00	$167.00
Purchase #3	$223.48	13.730%	$254.1638	$254.16	$254.15	$254.20
Purchase #4	$67.47	7.567%	$72.5755	$72.58	$72.60	$72.60
Purchase #5	$76.78	11.651%	$85.7256	$85.73	$85.75	$85.70
Purchase #6	$40.30	12.214%	$45.2222	$45.22	$45.20	$45.20
Purchase #7	$73.90	6.253%	$78.521	$78.52	$78.50	$78.50
7 purchase totals =	$719.71		$792.9663	$792.96	$792.95	$793.00