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	$164.86	8.344%	$178.6159	$178.62	$178.60	$178.60
Purchase #2	$41.31	10.838%	$45.7872	$45.79	$45.80	$45.80
Purchase #3	$136.61	4.517%	$142.7807	$142.78	$142.80	$142.80
Purchase #4	$159.93	5.131%	$168.136	$168.14	$168.15	$168.10
Purchase #5	$138.77	3.261%	$143.2953	$143.30	$143.30	$143.30
Purchase #6	$98.94	11.593%	$110.4101	$110.41	$110.40	$110.40
Purchase #7	$86.49	5.544%	$91.285	$91.29	$91.30	$91.30
7 purchase totals =	$826.91		$880.3102	$880.33	$880.35	$880.30