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	$243.29	11.679%	$271.7038	$271.70	$271.70	$271.70
Purchase #2	$76.98	12.376%	$86.507	$86.51	$86.50	$86.50
Purchase #3	$136.71	8.175%	$147.886	$147.89	$147.90	$147.90
Purchase #4	$221.89	5.607%	$234.3314	$234.33	$234.35	$234.30
Purchase #5	$250.82	4.553%	$262.2398	$262.24	$262.25	$262.20
Purchase #6	$162.34	12.489%	$182.6146	$182.61	$182.60	$182.60
Purchase #7	$47.98	11.647%	$53.5682	$53.57	$53.55	$53.60
7 purchase totals =	$1,140.01		$1,238.8508	$1,238.85	$1,238.85	$1,238.80