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	$120.92	7.628%	$130.1438	$130.14	$130.15	$130.10
Purchase #2	$156.95	11.711%	$175.3304	$175.33	$175.35	$175.30
Purchase #3	$66.40	9.286%	$72.5659	$72.57	$72.55	$72.60
Purchase #4	$222.46	6.192%	$236.2347	$236.23	$236.25	$236.20
Purchase #5	$162.60	4.729%	$170.2894	$170.29	$170.30	$170.30
Purchase #6	$73.52	10.619%	$81.3271	$81.33	$81.35	$81.30
Purchase #7	$95.31	5.439%	$100.4939	$100.49	$100.50	$100.50
7 purchase totals =	$898.16		$966.3852	$966.38	$966.45	$966.30