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	$126.91	10.115%	$139.7469	$139.75	$139.75	$139.70
Purchase #2	$41.86	12.306%	$47.0113	$47.01	$47.00	$47.00
Purchase #3	$40.76	12.261%	$45.7576	$45.76	$45.75	$45.80
Purchase #4	$233.86	6.154%	$248.2517	$248.25	$248.25	$248.30
Purchase #5	$65.66	6.871%	$70.1715	$70.17	$70.15	$70.20
Purchase #6	$244.92	4.741%	$256.5317	$256.53	$256.55	$256.50
Purchase #7	$188.80	10.824%	$209.2357	$209.24	$209.25	$209.20
7 purchase totals =	$942.77		$1,016.7064	$1,016.71	$1,016.70	$1,016.70