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	$204.39	8.518%	$221.7999	$221.80	$221.80	$221.80
Purchase #2	$227.40	9.126%	$248.1525	$248.15	$248.15	$248.20
Purchase #3	$128.84	5.673%	$136.1491	$136.15	$136.15	$136.10
Purchase #4	$22.41	12.321%	$25.1711	$25.17	$25.15	$25.20
Purchase #5	$246.52	11.356%	$274.5148	$274.51	$274.50	$274.50
Purchase #6	$69.56	4.256%	$72.5205	$72.52	$72.50	$72.50
Purchase #7	$93.83	7.243%	$100.6261	$100.63	$100.65	$100.60
7 purchase totals =	$992.95		$1,078.9340	$1,078.93	$1,078.90	$1,078.90