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	$69.92	10.810%	$77.4784	$77.48	$77.50	$77.50
Purchase #2	$146.55	12.156%	$164.3646	$164.36	$164.35	$164.40
Purchase #3	$122.28	7.607%	$131.5818	$131.58	$131.60	$131.60
Purchase #4	$124.62	6.238%	$132.3938	$132.39	$132.40	$132.40
Purchase #5	$148.46	4.339%	$154.9017	$154.90	$154.90	$154.90
Purchase #6	$89.82	7.463%	$96.5233	$96.52	$96.50	$96.50
Purchase #7	$187.98	12.435%	$211.3553	$211.36	$211.35	$211.40
7 purchase totals =	$889.63		$968.5989	$968.59	$968.60	$968.70