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	$213.38	6.116%	$226.4303	$226.43	$226.45	$226.40
Purchase #2	$114.27	11.732%	$127.6762	$127.68	$127.70	$127.70
Purchase #3	$89.56	10.479%	$98.945	$98.95	$98.95	$98.90
Purchase #4	$86.63	10.722%	$95.9185	$95.92	$95.90	$95.90
Purchase #5	$73.80	12.791%	$83.2398	$83.24	$83.25	$83.20
Purchase #6	$222.48	9.605%	$243.8492	$243.85	$243.85	$243.80
Purchase #7	$89.35	8.631%	$97.0618	$97.06	$97.05	$97.10
7 purchase totals =	$889.47		$973.1208	$973.13	$973.15	$973.00