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	$91.72	8.103%	$99.1521	$99.15	$99.15	$99.20
Purchase #2	$141.67	6.708%	$151.1732	$151.17	$151.15	$151.20
Purchase #3	$201.95	3.233%	$208.479	$208.48	$208.50	$208.50
Purchase #4	$97.59	6.229%	$103.6689	$103.67	$103.65	$103.70
Purchase #5	$83.64	9.396%	$91.4988	$91.50	$91.50	$91.50
Purchase #6	$128.50	10.762%	$142.3292	$142.33	$142.35	$142.30
Purchase #7	$108.29	4.220%	$112.8598	$112.86	$112.85	$112.90
7 purchase totals =	$853.36		$909.1610	$909.16	$909.15	$909.30