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	$231.57	3.740%	$240.2307	$240.23	$240.25	$240.20
Purchase #2	$142.67	12.164%	$160.0244	$160.02	$160.00	$160.00
Purchase #3	$101.86	9.839%	$111.882	$111.88	$111.90	$111.90
Purchase #4	$96.32	10.481%	$106.4153	$106.42	$106.40	$106.40
Purchase #5	$128.88	13.376%	$146.119	$146.12	$146.10	$146.10
Purchase #6	$120.63	12.107%	$135.2347	$135.23	$135.25	$135.20
Purchase #7	$75.78	9.116%	$82.6881	$82.69	$82.70	$82.70
7 purchase totals =	$897.71		$982.5942	$982.59	$982.60	$982.50