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	$26.67	8.216%	$28.8612	$28.86	$28.85	$28.90
Purchase #2	$250.40	12.145%	$280.8111	$280.81	$280.80	$280.80
Purchase #3	$165.82	5.111%	$174.2951	$174.30	$174.30	$174.30
Purchase #4	$141.52	8.752%	$153.9058	$153.91	$153.90	$153.90
Purchase #5	$244.92	5.131%	$257.4868	$257.49	$257.50	$257.50
Purchase #6	$85.56	6.170%	$90.8391	$90.84	$90.85	$90.80
Purchase #7	$14.84	11.469%	$16.542	$16.54	$16.55	$16.50
7 purchase totals =	$929.73		$1,002.7411	$1,002.75	$1,002.75	$1,002.70