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	$76.44	9.738%	$83.8837	$83.88	$83.90	$83.90
Purchase #2	$52.25	12.321%	$58.6877	$58.69	$58.70	$58.70
Purchase #3	$104.96	5.350%	$110.5754	$110.58	$110.60	$110.60
Purchase #4	$207.35	12.772%	$233.8327	$233.83	$233.85	$233.80
Purchase #5	$206.75	7.727%	$222.7256	$222.73	$222.75	$222.70
Purchase #6	$86.96	4.586%	$90.948	$90.95	$90.95	$90.90
Purchase #7	$39.83	10.131%	$43.8652	$43.87	$43.85	$43.90
7 purchase totals =	$774.54		$844.5183	$844.53	$844.60	$844.50