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	$31.40	6.688%	$33.5	$33.50	$33.50	$33.50
Purchase #2	$133.58	10.253%	$147.276	$147.28	$147.30	$147.30
Purchase #3	$179.50	9.605%	$196.741	$196.74	$196.75	$196.70
Purchase #4	$219.92	8.740%	$239.141	$239.14	$239.15	$239.10
Purchase #5	$120.77	3.770%	$125.323	$125.32	$125.30	$125.30
Purchase #6	$179.53	3.201%	$185.2768	$185.28	$185.30	$185.30
Purchase #7	$55.50	12.344%	$62.3509	$62.35	$62.35	$62.40
7 purchase totals =	$920.20		$989.6087	$989.61	$989.65	$989.60