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	$250.36	7.857%	$270.0308	$270.03	$270.05	$270.00
Purchase #2	$65.69	7.446%	$70.5813	$70.58	$70.60	$70.60
Purchase #3	$66.69	9.237%	$72.8502	$72.85	$72.85	$72.90
Purchase #4	$176.78	7.406%	$189.8723	$189.87	$189.85	$189.90
Purchase #5	$149.54	11.695%	$167.0287	$167.03	$167.05	$167.00
Purchase #6	$78.85	11.241%	$87.7135	$87.71	$87.70	$87.70
Purchase #7	$225.80	5.364%	$237.9119	$237.91	$237.90	$237.90
7 purchase totals =	$1,013.71		$1,095.9887	$1,095.98	$1,096.00	$1,096.00