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	$139.89	8.672%	$152.0213	$152.02	$152.00	$152.00
Purchase #2	$82.99	7.663%	$89.3495	$89.35	$89.35	$89.30
Purchase #3	$10.76	13.527%	$12.2155	$12.22	$12.20	$12.20
Purchase #4	$12.39	10.145%	$13.647	$13.65	$13.65	$13.60
Purchase #5	$40.98	13.582%	$46.5459	$46.55	$46.55	$46.50
Purchase #6	$109.40	5.754%	$115.6949	$115.69	$115.70	$115.70
Purchase #7	$113.87	13.768%	$129.5476	$129.55	$129.55	$129.50
7 purchase totals =	$510.28		$559.0217	$559.03	$559.00	$558.80