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	$236.51	6.501%	$251.8855	$251.89	$251.90	$251.90
Purchase #2	$64.40	10.576%	$71.2109	$71.21	$71.20	$71.20
Purchase #3	$242.47	3.287%	$250.44	$250.44	$250.45	$250.40
Purchase #4	$35.71	3.141%	$36.8317	$36.83	$36.85	$36.80
Purchase #5	$241.29	9.234%	$263.5707	$263.57	$263.55	$263.60
Purchase #6	$112.80	3.540%	$116.7931	$116.79	$116.80	$116.80
Purchase #7	$10.79	12.468%	$12.1353	$12.14	$12.15	$12.10
7 purchase totals =	$943.97		$1,002.8672	$1,002.87	$1,002.90	$1,002.80