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	$75.83	9.180%	$82.7912	$82.79	$82.80	$82.80
Purchase #2	$37.96	5.798%	$40.1609	$40.16	$40.15	$40.20
Purchase #3	$211.46	3.436%	$218.7258	$218.73	$218.75	$218.70
Purchase #4	$82.97	10.734%	$91.876	$91.88	$91.90	$91.90
Purchase #5	$24.72	9.432%	$27.0516	$27.05	$27.05	$27.10
Purchase #6	$247.72	11.859%	$277.0971	$277.10	$277.10	$277.10
Purchase #7	$52.50	13.249%	$59.4557	$59.46	$59.45	$59.50
7 purchase totals =	$733.16		$797.1583	$797.17	$797.20	$797.30