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	$35.46	12.507%	$39.895	$39.90	$39.90	$39.90
Purchase #2	$181.59	7.366%	$194.9659	$194.97	$194.95	$195.00
Purchase #3	$167.44	13.679%	$190.3441	$190.34	$190.35	$190.30
Purchase #4	$137.49	12.822%	$155.119	$155.12	$155.10	$155.10
Purchase #5	$74.38	4.426%	$77.6721	$77.67	$77.65	$77.70
Purchase #6	$121.83	4.746%	$127.6121	$127.61	$127.60	$127.60
Purchase #7	$152.90	9.798%	$167.8811	$167.88	$167.90	$167.90
7 purchase totals =	$871.09		$953.4893	$953.49	$953.45	$953.50