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	$39.54	8.365%	$42.8475	$42.85	$42.85	$42.80
Purchase #2	$78.49	9.262%	$85.7597	$85.76	$85.75	$85.80
Purchase #3	$148.38	8.419%	$160.8721	$160.87	$160.85	$160.90
Purchase #4	$186.82	13.598%	$212.2238	$212.22	$212.20	$212.20
Purchase #5	$84.61	3.217%	$87.3319	$87.33	$87.35	$87.30
Purchase #6	$96.85	9.201%	$105.7612	$105.76	$105.75	$105.80
Purchase #7	$83.61	6.252%	$88.8373	$88.84	$88.85	$88.80
7 purchase totals =	$718.30		$783.6335	$783.63	$783.60	$783.60