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	$90.77	6.737%	$96.8852	$96.89	$96.90	$96.90
Purchase #2	$79.72	6.691%	$85.0541	$85.05	$85.05	$85.10
Purchase #3	$220.31	8.292%	$238.5781	$238.58	$238.60	$238.60
Purchase #4	$116.60	5.701%	$123.2474	$123.25	$123.25	$123.20
Purchase #5	$183.60	3.165%	$189.4109	$189.41	$189.40	$189.40
Purchase #6	$33.25	11.708%	$37.1429	$37.14	$37.15	$37.10
Purchase #7	$157.79	11.742%	$176.3177	$176.32	$176.30	$176.30
7 purchase totals =	$882.04		$946.6363	$946.64	$946.65	$946.60