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	$48.69	5.259%	$51.2506	$51.25	$51.25	$51.30
Purchase #2	$43.57	13.870%	$49.6132	$49.61	$49.60	$49.60
Purchase #3	$153.39	9.639%	$168.1753	$168.18	$168.20	$168.20
Purchase #4	$248.83	8.404%	$269.7417	$269.74	$269.75	$269.70
Purchase #5	$50.61	13.584%	$57.4849	$57.48	$57.50	$57.50
Purchase #6	$175.96	10.390%	$194.2422	$194.24	$194.25	$194.20
Purchase #7	$78.55	3.774%	$81.5145	$81.51	$81.50	$81.50
7 purchase totals =	$799.60		$872.0224	$872.01	$872.05	$872.00