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	$76.29	9.184%	$83.2965	$83.30	$83.30	$83.30
Purchase #2	$244.77	9.782%	$268.7134	$268.71	$268.70	$268.70
Purchase #3	$228.49	12.227%	$256.4275	$256.43	$256.45	$256.40
Purchase #4	$156.95	5.599%	$165.7376	$165.74	$165.75	$165.70
Purchase #5	$102.84	9.440%	$112.5481	$112.55	$112.55	$112.50
Purchase #6	$184.27	4.687%	$192.9067	$192.91	$192.90	$192.90
Purchase #7	$30.40	5.779%	$32.1568	$32.16	$32.15	$32.20
7 purchase totals =	$1,024.01		$1,111.7866	$1,111.80	$1,111.80	$1,111.70