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	$95.63	10.256%	$105.4378	$105.44	$105.45	$105.40
Purchase #2	$204.66	8.659%	$222.3815	$222.38	$222.40	$222.40
Purchase #3	$209.61	7.667%	$225.6808	$225.68	$225.70	$225.70
Purchase #4	$91.26	13.764%	$103.821	$103.82	$103.80	$103.80
Purchase #5	$85.81	12.344%	$96.4024	$96.40	$96.40	$96.40
Purchase #6	$115.44	10.256%	$127.2795	$127.28	$127.30	$127.30
Purchase #7	$102.90	6.754%	$109.8499	$109.85	$109.85	$109.80
7 purchase totals =	$905.31		$990.8529	$990.85	$990.90	$990.80