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	$139.31	11.434%	$155.2387	$155.24	$155.25	$155.20
Purchase #2	$107.40	8.498%	$116.5269	$116.53	$116.55	$116.50
Purchase #3	$162.35	12.187%	$182.1356	$182.14	$182.15	$182.10
Purchase #4	$221.54	11.700%	$247.4602	$247.46	$247.45	$247.50
Purchase #5	$55.68	10.601%	$61.5826	$61.58	$61.60	$61.60
Purchase #6	$208.25	3.364%	$215.2555	$215.26	$215.25	$215.30
Purchase #7	$53.63	7.279%	$57.5337	$57.53	$57.55	$57.50
7 purchase totals =	$948.16		$1,035.7332	$1,035.74	$1,035.80	$1,035.70