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	$50.51	9.419%	$55.2675	$55.27	$55.25	$55.30
Purchase #2	$163.47	10.427%	$180.515	$180.52	$180.50	$180.50
Purchase #3	$49.55	7.625%	$53.3282	$53.33	$53.35	$53.30
Purchase #4	$104.36	7.282%	$111.9595	$111.96	$111.95	$112.00
Purchase #5	$139.72	4.755%	$146.3637	$146.36	$146.35	$146.40
Purchase #6	$151.38	12.456%	$170.2359	$170.24	$170.25	$170.20
Purchase #7	$136.67	6.333%	$145.3253	$145.33	$145.35	$145.30
7 purchase totals =	$795.66		$862.9951	$863.01	$863.00	$863.00