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	$8.52	7.562%	$9.1643	$9.16	$9.15	$9.20
Purchase #2	$96.35	3.504%	$99.7261	$99.73	$99.75	$99.70
Purchase #3	$51.61	3.516%	$53.4246	$53.42	$53.40	$53.40
Purchase #4	$59.60	4.638%	$62.3642	$62.36	$62.35	$62.40
Purchase #5	$228.59	8.641%	$248.3425	$248.34	$248.35	$248.30
Purchase #6	$37.44	7.632%	$40.2974	$40.30	$40.30	$40.30
Purchase #7	$124.46	10.498%	$137.5258	$137.53	$137.55	$137.50
7 purchase totals =	$606.57		$650.8449	$650.84	$650.85	$650.80