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	$33.65	11.344%	$37.4673	$37.47	$37.45	$37.50
Purchase #2	$164.32	7.358%	$176.4107	$176.41	$176.40	$176.40
Purchase #3	$80.43	10.321%	$88.7312	$88.73	$88.75	$88.70
Purchase #4	$179.28	5.609%	$189.3358	$189.34	$189.35	$189.30
Purchase #5	$27.90	13.470%	$31.6581	$31.66	$31.65	$31.70
Purchase #6	$133.59	9.801%	$146.6832	$146.68	$146.70	$146.70
Purchase #7	$130.73	11.793%	$146.147	$146.15	$146.15	$146.10
7 purchase totals =	$749.90		$816.4333	$816.44	$816.45	$816.40