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	$79.55	12.510%	$89.5017	$89.50	$89.50	$89.50
Purchase #2	$80.33	6.140%	$85.2623	$85.26	$85.25	$85.30
Purchase #3	$87.48	13.519%	$99.3064	$99.31	$99.30	$99.30
Purchase #4	$151.79	8.832%	$165.1961	$165.20	$165.20	$165.20
Purchase #5	$164.51	13.280%	$186.3569	$186.36	$186.35	$186.40
Purchase #6	$144.70	7.788%	$155.9692	$155.97	$155.95	$156.00
Purchase #7	$174.26	3.392%	$180.1709	$180.17	$180.15	$180.20
7 purchase totals =	$882.62		$961.7635	$961.77	$961.70	$961.90