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	$238.37	4.595%	$249.3231	$249.32	$249.30	$249.30
Purchase #2	$72.49	13.154%	$82.0253	$82.03	$82.05	$82.00
Purchase #3	$63.85	13.744%	$72.6255	$72.63	$72.65	$72.60
Purchase #4	$168.56	3.519%	$174.4916	$174.49	$174.50	$174.50
Purchase #5	$91.67	8.302%	$99.2804	$99.28	$99.30	$99.30
Purchase #6	$9.81	7.233%	$10.5196	$10.52	$10.50	$10.50
Purchase #7	$15.88	4.151%	$16.5392	$16.54	$16.55	$16.50
7 purchase totals =	$660.63		$704.8047	$704.81	$704.85	$704.70