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	$77.70	3.601%	$80.498	$80.50	$80.50	$80.50
Purchase #2	$6.96	5.316%	$7.33	$7.33	$7.35	$7.30
Purchase #3	$25.80	10.410%	$28.4858	$28.49	$28.50	$28.50
Purchase #4	$104.91	10.643%	$116.0756	$116.08	$116.10	$116.10
Purchase #5	$94.80	5.527%	$100.0396	$100.04	$100.05	$100.00
Purchase #6	$147.76	4.454%	$154.3412	$154.34	$154.35	$154.30
Purchase #7	$116.33	12.860%	$131.29	$131.29	$131.30	$131.30
7 purchase totals =	$574.26		$618.0602	$618.07	$618.15	$618.00