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	$50.96	3.217%	$52.5994	$52.60	$52.60	$52.60
Purchase #2	$78.30	6.519%	$83.4044	$83.40	$83.40	$83.40
Purchase #3	$120.31	13.486%	$136.535	$136.54	$136.55	$136.50
Purchase #4	$99.64	4.707%	$104.3301	$104.33	$104.35	$104.30
Purchase #5	$40.98	6.400%	$43.6027	$43.60	$43.60	$43.60
Purchase #6	$151.44	6.196%	$160.8232	$160.82	$160.80	$160.80
Purchase #7	$71.80	4.500%	$75.031	$75.03	$75.05	$75.00
7 purchase totals =	$613.43		$656.3258	$656.32	$656.35	$656.20