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	$91.86	8.370%	$99.5487	$99.55	$99.55	$99.50
Purchase #2	$100.39	3.439%	$103.8424	$103.84	$103.85	$103.80
Purchase #3	$97.61	5.140%	$102.6272	$102.63	$102.65	$102.60
Purchase #4	$201.27	4.762%	$210.8545	$210.85	$210.85	$210.90
Purchase #5	$131.72	9.557%	$144.3085	$144.31	$144.30	$144.30
Purchase #6	$162.98	9.339%	$178.2007	$178.20	$178.20	$178.20
Purchase #7	$43.38	13.119%	$49.071	$49.07	$49.05	$49.10
7 purchase totals =	$829.21		$888.4530	$888.45	$888.45	$888.40