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	$104.38	13.634%	$118.6112	$118.61	$118.60	$118.60
Purchase #2	$17.92	5.613%	$18.9258	$18.93	$18.95	$18.90
Purchase #3	$231.94	3.492%	$240.0393	$240.04	$240.05	$240.00
Purchase #4	$152.50	6.154%	$161.8849	$161.88	$161.90	$161.90
Purchase #5	$239.54	13.408%	$271.6575	$271.66	$271.65	$271.70
Purchase #6	$90.91	12.139%	$101.9456	$101.95	$101.95	$101.90
Purchase #7	$84.93	5.610%	$89.6946	$89.69	$89.70	$89.70
7 purchase totals =	$922.12		$1,002.7589	$1,002.76	$1,002.80	$1,002.70