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	$124.74	12.169%	$139.9196	$139.92	$139.90	$139.90
Purchase #2	$149.66	11.519%	$166.8993	$166.90	$166.90	$166.90
Purchase #3	$131.59	12.650%	$148.2361	$148.24	$148.25	$148.20
Purchase #4	$183.33	4.579%	$191.7247	$191.72	$191.70	$191.70
Purchase #5	$97.93	6.783%	$104.5726	$104.57	$104.55	$104.60
Purchase #6	$45.98	6.124%	$48.7958	$48.80	$48.80	$48.80
Purchase #7	$246.37	11.711%	$275.2224	$275.22	$275.20	$275.20
7 purchase totals =	$979.60		$1,075.3705	$1,075.37	$1,075.30	$1,075.30