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	$94.75	6.271%	$100.6918	$100.69	$100.70	$100.70
Purchase #2	$250.76	11.830%	$280.4249	$280.42	$280.40	$280.40
Purchase #3	$87.82	13.126%	$99.3473	$99.35	$99.35	$99.30
Purchase #4	$220.28	10.652%	$243.7442	$243.74	$243.75	$243.70
Purchase #5	$70.34	7.743%	$75.7864	$75.79	$75.80	$75.80
Purchase #6	$186.43	5.613%	$196.8943	$196.89	$196.90	$196.90
Purchase #7	$17.93	7.644%	$19.3006	$19.30	$19.30	$19.30
7 purchase totals =	$928.31		$1,016.1895	$1,016.18	$1,016.20	$1,016.10