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	$110.81	4.815%	$116.1455	$116.15	$116.15	$116.10
Purchase #2	$37.79	10.454%	$41.7406	$41.74	$41.75	$41.70
Purchase #3	$238.26	9.230%	$260.2514	$260.25	$260.25	$260.30
Purchase #4	$75.46	9.358%	$82.5215	$82.52	$82.50	$82.50
Purchase #5	$175.25	9.179%	$191.3362	$191.34	$191.35	$191.30
Purchase #6	$221.89	10.237%	$244.6049	$244.60	$244.60	$244.60
Purchase #7	$35.30	9.653%	$38.7075	$38.71	$38.70	$38.70
7 purchase totals =	$894.76		$975.3076	$975.31	$975.30	$975.20