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	$250.73	8.175%	$271.2272	$271.23	$271.25	$271.20
Purchase #2	$52.43	8.374%	$56.8205	$56.82	$56.80	$56.80
Purchase #3	$49.26	13.421%	$55.8712	$55.87	$55.85	$55.90
Purchase #4	$185.51	7.324%	$199.0968	$199.10	$199.10	$199.10
Purchase #5	$71.46	11.860%	$79.9352	$79.94	$79.95	$79.90
Purchase #6	$79.79	7.645%	$85.8899	$85.89	$85.90	$85.90
Purchase #7	$30.27	10.440%	$33.4302	$33.43	$33.45	$33.40
7 purchase totals =	$719.45		$782.2710	$782.28	$782.30	$782.20