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	$122.95	13.755%	$139.8618	$139.86	$139.85	$139.90
Purchase #2	$111.45	11.108%	$123.8299	$123.83	$123.85	$123.80
Purchase #3	$242.63	7.256%	$260.2352	$260.24	$260.25	$260.20
Purchase #4	$123.58	3.661%	$128.1043	$128.10	$128.10	$128.10
Purchase #5	$109.83	3.221%	$113.3676	$113.37	$113.35	$113.40
Purchase #6	$110.58	13.373%	$125.3679	$125.37	$125.35	$125.40
Purchase #7	$159.26	3.637%	$165.0523	$165.05	$165.05	$165.10
7 purchase totals =	$980.28		$1,055.8190	$1,055.82	$1,055.80	$1,055.90