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	$18.81	9.849%	$20.6626	$20.66	$20.65	$20.70
Purchase #2	$226.28	4.802%	$237.146	$237.15	$237.15	$237.10
Purchase #3	$105.40	12.791%	$118.8817	$118.88	$118.90	$118.90
Purchase #4	$42.43	11.359%	$47.2496	$47.25	$47.25	$47.20
Purchase #5	$250.67	13.573%	$284.6934	$284.69	$284.70	$284.70
Purchase #6	$38.90	11.128%	$43.2288	$43.23	$43.25	$43.20
Purchase #7	$231.57	11.765%	$258.8142	$258.81	$258.80	$258.80
7 purchase totals =	$914.06		$1,010.6763	$1,010.67	$1,010.70	$1,010.60