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	$43.61	4.172%	$45.4294	$45.43	$45.45	$45.40
Purchase #2	$48.90	8.443%	$53.0286	$53.03	$53.05	$53.00
Purchase #3	$244.51	7.579%	$263.0414	$263.04	$263.05	$263.00
Purchase #4	$197.69	4.359%	$206.3073	$206.31	$206.30	$206.30
Purchase #5	$124.41	12.474%	$139.9289	$139.93	$139.95	$139.90
Purchase #6	$93.54	7.807%	$100.8427	$100.84	$100.85	$100.80
Purchase #7	$19.72	5.522%	$20.8089	$20.81	$20.80	$20.80
7 purchase totals =	$772.38		$829.3872	$829.39	$829.45	$829.20