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	$98.51	13.597%	$111.9044	$111.90	$111.90	$111.90
Purchase #2	$33.71	13.618%	$38.3006	$38.30	$38.30	$38.30
Purchase #3	$222.95	11.797%	$249.2514	$249.25	$249.25	$249.30
Purchase #4	$36.70	5.350%	$38.6635	$38.66	$38.65	$38.70
Purchase #5	$137.76	11.248%	$153.2552	$153.26	$153.25	$153.30
Purchase #6	$218.57	9.809%	$240.0095	$240.01	$240.00	$240.00
Purchase #7	$247.76	3.266%	$255.8518	$255.85	$255.85	$255.90
7 purchase totals =	$995.96		$1,087.2364	$1,087.23	$1,087.20	$1,087.40