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	$234.87	12.419%	$264.0385	$264.04	$264.05	$264.00
Purchase #2	$61.29	4.586%	$64.1008	$64.10	$64.10	$64.10
Purchase #3	$151.83	11.145%	$168.7515	$168.75	$168.75	$168.80
Purchase #4	$50.37	11.525%	$56.1751	$56.18	$56.20	$56.20
Purchase #5	$177.89	10.295%	$196.2038	$196.20	$196.20	$196.20
Purchase #6	$168.71	6.455%	$179.6002	$179.60	$179.60	$179.60
Purchase #7	$42.61	12.796%	$48.0624	$48.06	$48.05	$48.10
7 purchase totals =	$887.57		$976.9323	$976.93	$976.95	$977.00