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	$37.47	13.184%	$42.41	$42.41	$42.40	$42.40
Purchase #2	$174.82	9.728%	$191.8265	$191.83	$191.85	$191.80
Purchase #3	$207.60	4.221%	$216.3628	$216.36	$216.35	$216.40
Purchase #4	$144.82	7.843%	$156.1782	$156.18	$156.20	$156.20
Purchase #5	$155.28	10.448%	$171.5037	$171.50	$171.50	$171.50
Purchase #6	$44.39	10.793%	$49.181	$49.18	$49.20	$49.20
Purchase #7	$32.92	11.702%	$36.7723	$36.77	$36.75	$36.80
7 purchase totals =	$797.30		$864.2345	$864.23	$864.25	$864.30