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	$84.81	4.659%	$88.7613	$88.76	$88.75	$88.80
Purchase #2	$140.91	13.758%	$160.2964	$160.30	$160.30	$160.30
Purchase #3	$30.50	10.269%	$33.632	$33.63	$33.65	$33.60
Purchase #4	$7.43	5.263%	$7.821	$7.82	$7.80	$7.80
Purchase #5	$138.33	7.644%	$148.9039	$148.90	$148.90	$148.90
Purchase #6	$55.68	10.603%	$61.5838	$61.58	$61.60	$61.60
Purchase #7	$18.54	4.719%	$19.4149	$19.41	$19.40	$19.40
7 purchase totals =	$476.20		$520.4133	$520.40	$520.40	$520.40