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	$83.80	7.760%	$90.3029	$90.30	$90.30	$90.30
Purchase #2	$55.32	6.579%	$58.9595	$58.96	$58.95	$59.00
Purchase #3	$134.32	9.807%	$147.4928	$147.49	$147.50	$147.50
Purchase #4	$12.61	4.225%	$13.1428	$13.14	$13.15	$13.10
Purchase #5	$8.61	10.544%	$9.5178	$9.52	$9.50	$9.50
Purchase #6	$65.84	9.720%	$72.2396	$72.24	$72.25	$72.20
Purchase #7	$137.74	13.869%	$156.8432	$156.84	$156.85	$156.80
7 purchase totals =	$498.24		$548.4986	$548.49	$548.50	$548.40