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	$146.84	5.433%	$154.8178	$154.82	$154.80	$154.80
Purchase #2	$156.43	9.522%	$171.3253	$171.33	$171.35	$171.30
Purchase #3	$17.69	4.492%	$18.4846	$18.48	$18.50	$18.50
Purchase #4	$94.39	5.838%	$99.9005	$99.90	$99.90	$99.90
Purchase #5	$171.65	9.783%	$188.4425	$188.44	$188.45	$188.40
Purchase #6	$159.33	3.500%	$164.9066	$164.91	$164.90	$164.90
Purchase #7	$41.41	13.869%	$47.1532	$47.15	$47.15	$47.20
7 purchase totals =	$787.74		$845.0305	$845.03	$845.05	$845.00