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	$45.70	5.710%	$48.3095	$48.31	$48.30	$48.30
Purchase #2	$36.71	6.404%	$39.0609	$39.06	$39.05	$39.10
Purchase #3	$224.95	11.776%	$251.4401	$251.44	$251.45	$251.40
Purchase #4	$51.29	6.160%	$54.4495	$54.45	$54.45	$54.40
Purchase #5	$201.38	3.790%	$209.0123	$209.01	$209.00	$209.00
Purchase #6	$31.52	5.870%	$33.3702	$33.37	$33.35	$33.40
Purchase #7	$10.73	11.393%	$11.9525	$11.95	$11.95	$12.00
7 purchase totals =	$602.28		$647.5950	$647.59	$647.55	$647.60