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	$186.45	12.244%	$209.2789	$209.28	$209.30	$209.30
Purchase #2	$242.31	3.426%	$250.6115	$250.61	$250.60	$250.60
Purchase #3	$47.39	3.155%	$48.8852	$48.89	$48.90	$48.90
Purchase #4	$150.97	3.734%	$156.6072	$156.61	$156.60	$156.60
Purchase #5	$90.84	4.495%	$94.9233	$94.92	$94.90	$94.90
Purchase #6	$81.99	5.766%	$86.7175	$86.72	$86.70	$86.70
Purchase #7	$73.55	7.591%	$79.1332	$79.13	$79.15	$79.10
7 purchase totals =	$873.50		$926.1568	$926.16	$926.15	$926.10