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	$243.51	11.841%	$272.344	$272.34	$272.35	$272.30
Purchase #2	$192.84	7.575%	$207.4476	$207.45	$207.45	$207.40
Purchase #3	$136.27	3.151%	$140.5639	$140.56	$140.55	$140.60
Purchase #4	$89.47	13.237%	$101.3131	$101.31	$101.30	$101.30
Purchase #5	$96.86	8.361%	$104.9585	$104.96	$104.95	$105.00
Purchase #6	$49.77	4.392%	$51.9559	$51.96	$51.95	$52.00
Purchase #7	$115.90	13.300%	$131.3147	$131.31	$131.30	$131.30
7 purchase totals =	$924.62		$1,009.8977	$1,009.89	$1,009.85	$1,009.90