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	$75.58	3.681%	$78.3621	$78.36	$78.35	$78.40
Purchase #2	$99.47	10.369%	$109.784	$109.78	$109.80	$109.80
Purchase #3	$66.89	8.522%	$72.5904	$72.59	$72.60	$72.60
Purchase #4	$210.85	4.448%	$220.2286	$220.23	$220.25	$220.20
Purchase #5	$27.99	5.805%	$29.6148	$29.61	$29.60	$29.60
Purchase #6	$159.44	11.649%	$178.0132	$178.01	$178.00	$178.00
Purchase #7	$150.80	4.363%	$157.3794	$157.38	$157.40	$157.40
7 purchase totals =	$791.02		$845.9725	$845.96	$846.00	$846.00