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	$172.41	9.474%	$188.7441	$188.74	$188.75	$188.70
Purchase #2	$139.67	11.640%	$155.9276	$155.93	$155.95	$155.90
Purchase #3	$127.45	10.287%	$140.5608	$140.56	$140.55	$140.60
Purchase #4	$77.85	4.187%	$81.1096	$81.11	$81.10	$81.10
Purchase #5	$54.69	12.851%	$61.7182	$61.72	$61.70	$61.70
Purchase #6	$49.74	3.321%	$51.3919	$51.39	$51.40	$51.40
Purchase #7	$98.31	6.729%	$104.9253	$104.93	$104.95	$104.90
7 purchase totals =	$720.12		$784.3775	$784.38	$784.40	$784.30