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	$79.84	12.223%	$89.5988	$89.60	$89.60	$89.60
Purchase #2	$5.82	9.106%	$6.35	$6.35	$6.35	$6.40
Purchase #3	$212.25	13.187%	$240.2394	$240.24	$240.25	$240.20
Purchase #4	$244.29	11.533%	$272.464	$272.46	$272.45	$272.50
Purchase #5	$137.69	13.462%	$156.2258	$156.23	$156.25	$156.20
Purchase #6	$144.77	6.300%	$153.8905	$153.89	$153.90	$153.90
Purchase #7	$36.62	11.310%	$40.7617	$40.76	$40.75	$40.80
7 purchase totals =	$861.28		$959.5302	$959.53	$959.55	$959.60