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	$202.53	6.460%	$215.6134	$215.61	$215.60	$215.60
Purchase #2	$124.81	11.369%	$138.9996	$139.00	$139.00	$139.00
Purchase #3	$165.88	3.605%	$171.86	$171.86	$171.85	$171.90
Purchase #4	$151.82	10.712%	$168.083	$168.08	$168.10	$168.10
Purchase #5	$97.42	7.442%	$104.67	$104.67	$104.65	$104.70
Purchase #6	$129.49	8.647%	$140.687	$140.69	$140.70	$140.70
Purchase #7	$73.52	9.304%	$80.3603	$80.36	$80.35	$80.40
7 purchase totals =	$945.47		$1,020.2733	$1,020.27	$1,020.25	$1,020.40