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	$203.84	12.111%	$228.5271	$228.53	$228.55	$228.50
Purchase #2	$173.84	6.693%	$185.4751	$185.48	$185.50	$185.50
Purchase #3	$146.26	3.791%	$151.8047	$151.80	$151.80	$151.80
Purchase #4	$78.32	7.127%	$83.9019	$83.90	$83.90	$83.90
Purchase #5	$97.84	12.127%	$109.7051	$109.71	$109.70	$109.70
Purchase #6	$230.71	5.190%	$242.6838	$242.68	$242.70	$242.70
Purchase #7	$85.63	3.841%	$88.919	$88.92	$88.90	$88.90
7 purchase totals =	$1,016.44		$1,091.0167	$1,091.02	$1,091.05	$1,091.00