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	$246.38	4.267%	$256.893	$256.89	$256.90	$256.90
Purchase #2	$127.76	3.607%	$132.3683	$132.37	$132.35	$132.40
Purchase #3	$142.98	3.666%	$148.2216	$148.22	$148.20	$148.20
Purchase #4	$43.70	10.809%	$48.4235	$48.42	$48.40	$48.40
Purchase #5	$98.86	13.603%	$112.3079	$112.31	$112.30	$112.30
Purchase #6	$207.54	13.404%	$235.3587	$235.36	$235.35	$235.40
Purchase #7	$216.47	4.279%	$225.7328	$225.73	$225.75	$225.70
7 purchase totals =	$1,083.69		$1,159.3058	$1,159.30	$1,159.25	$1,159.30