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	$74.48	4.144%	$77.5665	$77.57	$77.55	$77.60
Purchase #2	$101.73	7.341%	$109.198	$109.20	$109.20	$109.20
Purchase #3	$18.61	12.242%	$20.8882	$20.89	$20.90	$20.90
Purchase #4	$26.91	10.624%	$29.7689	$29.77	$29.75	$29.80
Purchase #5	$26.56	5.654%	$28.0617	$28.06	$28.05	$28.10
Purchase #6	$19.35	10.595%	$21.4001	$21.40	$21.40	$21.40
Purchase #7	$33.31	12.746%	$37.5557	$37.56	$37.55	$37.60
7 purchase totals =	$300.95		$324.4391	$324.45	$324.40	$324.60