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	$225.77	4.350%	$235.591	$235.59	$235.60	$235.60
Purchase #2	$98.95	10.322%	$109.1636	$109.16	$109.15	$109.20
Purchase #3	$25.84	10.353%	$28.5152	$28.52	$28.50	$28.50
Purchase #4	$174.68	12.155%	$195.9124	$195.91	$195.90	$195.90
Purchase #5	$71.48	6.866%	$76.3878	$76.39	$76.40	$76.40
Purchase #6	$160.74	7.328%	$172.519	$172.52	$172.50	$172.50
Purchase #7	$63.79	13.630%	$72.4846	$72.48	$72.50	$72.50
7 purchase totals =	$821.25		$890.5736	$890.57	$890.55	$890.60