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	$85.61	6.284%	$90.9897	$90.99	$91.00	$91.00
Purchase #2	$207.76	3.593%	$215.2248	$215.22	$215.20	$215.20
Purchase #3	$40.80	6.185%	$43.3235	$43.32	$43.30	$43.30
Purchase #4	$112.35	13.859%	$127.9206	$127.92	$127.90	$127.90
Purchase #5	$57.54	10.825%	$63.7687	$63.77	$63.75	$63.80
Purchase #6	$143.72	11.518%	$160.2737	$160.27	$160.25	$160.30
Purchase #7	$216.70	12.819%	$244.4788	$244.48	$244.50	$244.50
7 purchase totals =	$864.48		$945.9798	$945.97	$945.90	$946.00