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	$142.86	12.294%	$160.4232	$160.42	$160.40	$160.40
Purchase #2	$91.98	4.436%	$96.0602	$96.06	$96.05	$96.10
Purchase #3	$123.43	8.330%	$133.7117	$133.71	$133.70	$133.70
Purchase #4	$42.91	4.563%	$44.868	$44.87	$44.85	$44.90
Purchase #5	$83.82	3.614%	$86.8493	$86.85	$86.85	$86.80
Purchase #6	$209.37	9.532%	$229.3271	$229.33	$229.35	$229.30
Purchase #7	$95.27	4.364%	$99.4276	$99.43	$99.45	$99.40
7 purchase totals =	$789.64		$850.6671	$850.67	$850.65	$850.60