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	$55.48	6.420%	$59.0418	$59.04	$59.05	$59.00
Purchase #2	$55.82	10.822%	$61.8608	$61.86	$61.85	$61.90
Purchase #3	$179.46	11.797%	$200.6309	$200.63	$200.65	$200.60
Purchase #4	$10.32	8.109%	$11.1568	$11.16	$11.15	$11.20
Purchase #5	$138.61	12.129%	$155.422	$155.42	$155.40	$155.40
Purchase #6	$40.91	10.799%	$45.3279	$45.33	$45.35	$45.30
Purchase #7	$205.75	13.413%	$233.3472	$233.35	$233.35	$233.30
7 purchase totals =	$686.35		$766.7874	$766.79	$766.80	$766.70