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	$124.92	3.461%	$129.2435	$129.24	$129.25	$129.20
Purchase #2	$128.32	9.666%	$140.7234	$140.72	$140.70	$140.70
Purchase #3	$104.83	5.288%	$110.3734	$110.37	$110.35	$110.40
Purchase #4	$177.33	4.629%	$185.5386	$185.54	$185.55	$185.50
Purchase #5	$220.56	9.758%	$242.0822	$242.08	$242.10	$242.10
Purchase #6	$197.92	6.571%	$210.9253	$210.93	$210.95	$210.90
Purchase #7	$124.46	5.849%	$131.7397	$131.74	$131.75	$131.70
7 purchase totals =	$1,078.34		$1,150.6261	$1,150.62	$1,150.65	$1,150.50