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	$48.57	4.560%	$50.7848	$50.78	$50.80	$50.80
Purchase #2	$250.35	12.760%	$282.2947	$282.29	$282.30	$282.30
Purchase #3	$145.38	8.556%	$157.8187	$157.82	$157.80	$157.80
Purchase #4	$112.78	9.117%	$123.0622	$123.06	$123.05	$123.10
Purchase #5	$191.82	7.333%	$205.8862	$205.89	$205.90	$205.90
Purchase #6	$83.58	9.384%	$91.4231	$91.42	$91.40	$91.40
Purchase #7	$153.60	13.410%	$174.1978	$174.20	$174.20	$174.20
7 purchase totals =	$986.08		$1,085.4675	$1,085.46	$1,085.45	$1,085.50