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	$45.51	11.809%	$50.8843	$50.88	$50.90	$50.90
Purchase #2	$114.36	8.386%	$123.9502	$123.95	$123.95	$124.00
Purchase #3	$47.96	4.162%	$49.9561	$49.96	$49.95	$50.00
Purchase #4	$77.69	11.726%	$86.7999	$86.80	$86.80	$86.80
Purchase #5	$97.56	9.296%	$106.6292	$106.63	$106.65	$106.60
Purchase #6	$92.42	6.546%	$98.4698	$98.47	$98.45	$98.50
Purchase #7	$15.34	3.392%	$15.8603	$15.86	$15.85	$15.90
7 purchase totals =	$490.84		$532.5498	$532.55	$532.55	$532.70