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	$56.52	5.119%	$59.4133	$59.41	$59.40	$59.40
Purchase #2	$134.96	6.114%	$143.2115	$143.21	$143.20	$143.20
Purchase #3	$171.56	5.730%	$181.3904	$181.39	$181.40	$181.40
Purchase #4	$104.91	10.412%	$115.8332	$115.83	$115.85	$115.80
Purchase #5	$57.93	8.332%	$62.7567	$62.76	$62.75	$62.80
Purchase #6	$35.92	4.757%	$37.6287	$37.63	$37.65	$37.60
Purchase #7	$57.36	6.791%	$61.2553	$61.26	$61.25	$61.30
7 purchase totals =	$619.16		$661.4891	$661.49	$661.50	$661.50