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	$115.59	12.742%	$130.3185	$130.32	$130.30	$130.30
Purchase #2	$227.92	4.751%	$238.7485	$238.75	$238.75	$238.70
Purchase #3	$29.36	10.139%	$32.3368	$32.34	$32.35	$32.30
Purchase #4	$144.86	8.323%	$156.9167	$156.92	$156.90	$156.90
Purchase #5	$69.54	11.131%	$77.2805	$77.28	$77.30	$77.30
Purchase #6	$60.37	9.188%	$65.9168	$65.92	$65.90	$65.90
Purchase #7	$42.31	12.155%	$47.4528	$47.45	$47.45	$47.50
7 purchase totals =	$689.95		$748.9706	$748.98	$748.95	$748.90