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	$153.82	4.578%	$160.8619	$160.86	$160.85	$160.90
Purchase #2	$49.89	10.516%	$55.1364	$55.14	$55.15	$55.10
Purchase #3	$150.75	8.519%	$163.5924	$163.59	$163.60	$163.60
Purchase #4	$190.53	3.299%	$196.8156	$196.82	$196.80	$196.80
Purchase #5	$201.83	8.730%	$219.4498	$219.45	$219.45	$219.40
Purchase #6	$29.79	10.343%	$32.8712	$32.87	$32.85	$32.90
Purchase #7	$28.25	3.808%	$29.3258	$29.33	$29.35	$29.30
7 purchase totals =	$804.86		$858.0531	$858.06	$858.05	$858.00