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	$163.74	11.804%	$183.0679	$183.07	$183.05	$183.10
Purchase #2	$147.25	9.315%	$160.9663	$160.97	$160.95	$161.00
Purchase #3	$24.62	10.228%	$27.1381	$27.14	$27.15	$27.10
Purchase #4	$85.30	6.269%	$90.6475	$90.65	$90.65	$90.60
Purchase #5	$195.78	13.427%	$222.0674	$222.07	$222.05	$222.10
Purchase #6	$11.27	10.702%	$12.4761	$12.48	$12.50	$12.50
Purchase #7	$85.77	4.421%	$89.5619	$89.56	$89.55	$89.60
7 purchase totals =	$713.73		$785.9252	$785.94	$785.90	$786.00