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	$82.71	9.224%	$90.3392	$90.34	$90.35	$90.30
Purchase #2	$227.59	5.728%	$240.6264	$240.63	$240.65	$240.60
Purchase #3	$234.59	5.370%	$247.1875	$247.19	$247.20	$247.20
Purchase #4	$120.78	5.339%	$127.2284	$127.23	$127.25	$127.20
Purchase #5	$95.78	11.132%	$106.4422	$106.44	$106.45	$106.40
Purchase #6	$33.59	9.140%	$36.6601	$36.66	$36.65	$36.70
Purchase #7	$32.36	12.864%	$36.5228	$36.52	$36.50	$36.50
7 purchase totals =	$827.40		$885.0066	$885.01	$885.05	$884.90