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	$80.54	10.839%	$89.2697	$89.27	$89.25	$89.30
Purchase #2	$96.89	6.398%	$103.089	$103.09	$103.10	$103.10
Purchase #3	$209.42	11.155%	$232.7808	$232.78	$232.80	$232.80
Purchase #4	$143.90	10.871%	$159.5434	$159.54	$159.55	$159.50
Purchase #5	$234.32	6.647%	$249.8953	$249.90	$249.90	$249.90
Purchase #6	$26.68	13.706%	$30.3368	$30.34	$30.35	$30.30
Purchase #7	$37.66	6.275%	$40.0232	$40.02	$40.00	$40.00
7 purchase totals =	$829.41		$904.9382	$904.94	$904.95	$904.90