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	$84.96	8.727%	$92.3745	$92.37	$92.35	$92.40
Purchase #2	$85.71	4.738%	$89.7709	$89.77	$89.75	$89.80
Purchase #3	$180.70	8.488%	$196.0378	$196.04	$196.05	$196.00
Purchase #4	$77.46	10.248%	$85.3981	$85.40	$85.40	$85.40
Purchase #5	$237.65	13.853%	$270.5717	$270.57	$270.55	$270.60
Purchase #6	$205.29	9.690%	$225.1826	$225.18	$225.20	$225.20
Purchase #7	$98.84	12.846%	$111.537	$111.54	$111.55	$111.50
7 purchase totals =	$970.61		$1,070.8726	$1,070.87	$1,070.85	$1,070.90