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	$33.83	13.412%	$38.3673	$38.37	$38.35	$38.40
Purchase #2	$185.57	3.343%	$191.7736	$191.77	$191.75	$191.80
Purchase #3	$225.93	7.128%	$242.0343	$242.03	$242.05	$242.00
Purchase #4	$206.79	5.578%	$218.3247	$218.32	$218.30	$218.30
Purchase #5	$180.63	13.721%	$205.4142	$205.41	$205.40	$205.40
Purchase #6	$26.37	13.343%	$29.8885	$29.89	$29.90	$29.90
Purchase #7	$214.51	4.853%	$224.9202	$224.92	$224.90	$224.90
7 purchase totals =	$1,073.63		$1,150.7228	$1,150.71	$1,150.65	$1,150.70