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	$88.97	10.526%	$98.335	$98.34	$98.35	$98.30
Purchase #2	$109.59	13.457%	$124.3375	$124.34	$124.35	$124.30
Purchase #3	$234.95	8.242%	$254.3146	$254.31	$254.30	$254.30
Purchase #4	$84.74	6.455%	$90.21	$90.21	$90.20	$90.20
Purchase #5	$162.50	11.148%	$180.6155	$180.62	$180.60	$180.60
Purchase #6	$18.53	9.613%	$20.3113	$20.31	$20.30	$20.30
Purchase #7	$122.34	7.598%	$131.6354	$131.64	$131.65	$131.60
7 purchase totals =	$821.62		$899.7593	$899.77	$899.75	$899.60