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	$19.51	4.277%	$20.3444	$20.34	$20.35	$20.30
Purchase #2	$116.33	12.796%	$131.2156	$131.22	$131.20	$131.20
Purchase #3	$26.82	6.224%	$28.4893	$28.49	$28.50	$28.50
Purchase #4	$115.81	5.730%	$122.4459	$122.45	$122.45	$122.40
Purchase #5	$101.78	3.121%	$104.9566	$104.96	$104.95	$105.00
Purchase #6	$5.36	3.236%	$5.5334	$5.53	$5.55	$5.50
Purchase #7	$100.42	9.204%	$109.6627	$109.66	$109.65	$109.70
7 purchase totals =	$486.03		$522.6479	$522.65	$522.65	$522.60