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	$90.76	6.437%	$96.6022	$96.60	$96.60	$96.60
Purchase #2	$74.56	5.287%	$78.502	$78.50	$78.50	$78.50
Purchase #3	$73.60	13.463%	$83.5088	$83.51	$83.50	$83.50
Purchase #4	$154.93	13.764%	$176.2546	$176.25	$176.25	$176.30
Purchase #5	$201.72	8.737%	$219.3443	$219.34	$219.35	$219.30
Purchase #6	$79.77	11.275%	$88.7641	$88.76	$88.75	$88.80
Purchase #7	$43.77	13.419%	$49.6435	$49.64	$49.65	$49.60
7 purchase totals =	$719.11		$792.6195	$792.60	$792.60	$792.60