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	$186.92	6.214%	$198.5352	$198.54	$198.55	$198.50
Purchase #2	$39.47	10.701%	$43.6937	$43.69	$43.70	$43.70
Purchase #3	$51.98	10.411%	$57.3916	$57.39	$57.40	$57.40
Purchase #4	$182.69	7.815%	$196.9672	$196.97	$196.95	$197.00
Purchase #5	$45.61	8.783%	$49.6159	$49.62	$49.60	$49.60
Purchase #6	$80.97	11.573%	$90.3407	$90.34	$90.35	$90.30
Purchase #7	$13.62	12.816%	$15.3655	$15.37	$15.35	$15.40
7 purchase totals =	$601.26		$651.9098	$651.92	$651.90	$651.90