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	$101.76	11.417%	$113.3779	$113.38	$113.40	$113.40
Purchase #2	$195.51	12.392%	$219.7376	$219.74	$219.75	$219.70
Purchase #3	$105.35	7.500%	$113.2513	$113.25	$113.25	$113.30
Purchase #4	$82.30	12.261%	$92.3908	$92.39	$92.40	$92.40
Purchase #5	$20.34	5.609%	$21.4809	$21.48	$21.50	$21.50
Purchase #6	$150.82	9.492%	$165.1358	$165.14	$165.15	$165.10
Purchase #7	$53.73	7.152%	$57.5728	$57.57	$57.55	$57.60
7 purchase totals =	$709.81		$782.9471	$782.95	$783.00	$783.00