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	$117.76	4.846%	$123.4666	$123.47	$123.45	$123.50
Purchase #2	$187.55	12.133%	$210.3054	$210.31	$210.30	$210.30
Purchase #3	$236.37	12.630%	$266.2235	$266.22	$266.20	$266.20
Purchase #4	$112.48	6.584%	$119.8857	$119.89	$119.90	$119.90
Purchase #5	$248.43	6.357%	$264.2227	$264.22	$264.20	$264.20
Purchase #6	$205.86	4.688%	$215.5107	$215.51	$215.50	$215.50
Purchase #7	$62.73	12.532%	$70.5913	$70.59	$70.60	$70.60
7 purchase totals =	$1,171.18		$1,270.2059	$1,270.21	$1,270.15	$1,270.20