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	$220.64	13.412%	$250.2322	$250.23	$250.25	$250.20
Purchase #2	$176.48	11.179%	$196.2087	$196.21	$196.20	$196.20
Purchase #3	$82.26	9.324%	$89.9299	$89.93	$89.95	$89.90
Purchase #4	$16.94	7.371%	$18.1886	$18.19	$18.20	$18.20
Purchase #5	$186.95	11.712%	$208.8456	$208.85	$208.85	$208.80
Purchase #6	$184.32	11.321%	$205.1869	$205.19	$205.20	$205.20
Purchase #7	$132.39	11.451%	$147.55	$147.55	$147.55	$147.60
7 purchase totals =	$999.98		$1,116.1419	$1,116.15	$1,116.20	$1,116.10