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	$44.35	10.814%	$49.146	$49.15	$49.15	$49.10
Purchase #2	$85.29	3.602%	$88.3621	$88.36	$88.35	$88.40
Purchase #3	$37.89	10.522%	$41.8768	$41.88	$41.90	$41.90
Purchase #4	$10.72	9.519%	$11.7404	$11.74	$11.75	$11.70
Purchase #5	$221.66	12.789%	$250.0081	$250.01	$250.00	$250.00
Purchase #6	$52.59	13.690%	$59.7896	$59.79	$59.80	$59.80
Purchase #7	$234.89	6.374%	$249.8619	$249.86	$249.85	$249.90
7 purchase totals =	$687.39		$750.7849	$750.79	$750.80	$750.80