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	$246.89	4.354%	$257.6396	$257.64	$257.65	$257.60
Purchase #2	$188.46	11.258%	$209.6768	$209.68	$209.70	$209.70
Purchase #3	$124.32	7.812%	$134.0319	$134.03	$134.05	$134.00
Purchase #4	$136.83	4.331%	$142.7561	$142.76	$142.75	$142.80
Purchase #5	$33.53	12.587%	$37.7504	$37.75	$37.75	$37.80
Purchase #6	$77.96	9.644%	$85.4785	$85.48	$85.50	$85.50
Purchase #7	$119.73	12.405%	$134.5825	$134.58	$134.60	$134.60
7 purchase totals =	$927.72		$1,001.9158	$1,001.92	$1,002.00	$1,002.00