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	$203.89	7.251%	$218.6741	$218.67	$218.65	$218.70
Purchase #2	$132.62	13.187%	$150.1086	$150.11	$150.10	$150.10
Purchase #3	$113.28	9.385%	$123.9113	$123.91	$123.90	$123.90
Purchase #4	$45.57	12.542%	$51.2854	$51.29	$51.30	$51.30
Purchase #5	$82.81	3.846%	$85.9949	$85.99	$86.00	$86.00
Purchase #6	$207.88	4.517%	$217.2699	$217.27	$217.25	$217.30
Purchase #7	$137.50	10.519%	$151.9636	$151.96	$151.95	$152.00
7 purchase totals =	$923.55		$999.2078	$999.20	$999.15	$999.30