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	$245.86	9.870%	$270.1264	$270.13	$270.15	$270.10
Purchase #2	$55.79	5.792%	$59.0214	$59.02	$59.00	$59.00
Purchase #3	$193.31	13.855%	$220.0931	$220.09	$220.10	$220.10
Purchase #4	$241.83	10.521%	$267.2729	$267.27	$267.25	$267.30
Purchase #5	$86.74	4.254%	$90.4299	$90.43	$90.45	$90.40
Purchase #6	$45.48	6.126%	$48.2661	$48.27	$48.25	$48.30
Purchase #7	$174.33	3.639%	$180.6739	$180.67	$180.65	$180.70
7 purchase totals =	$1,043.34		$1,135.8837	$1,135.88	$1,135.85	$1,135.90