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	$188.68	6.117%	$200.2216	$200.22	$200.20	$200.20
Purchase #2	$67.89	3.821%	$70.4841	$70.48	$70.50	$70.50
Purchase #3	$18.71	10.331%	$20.6429	$20.64	$20.65	$20.60
Purchase #4	$36.48	6.428%	$38.8249	$38.82	$38.80	$38.80
Purchase #5	$39.90	8.689%	$43.3669	$43.37	$43.35	$43.40
Purchase #6	$241.95	10.729%	$267.9088	$267.91	$267.90	$267.90
Purchase #7	$245.45	13.856%	$279.4596	$279.46	$279.45	$279.50
7 purchase totals =	$839.06		$920.9088	$920.90	$920.85	$920.90