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	$234.73	12.452%	$263.9586	$263.96	$263.95	$264.00
Purchase #2	$46.71	5.649%	$49.3486	$49.35	$49.35	$49.30
Purchase #3	$36.33	11.232%	$40.4106	$40.41	$40.40	$40.40
Purchase #4	$219.67	7.126%	$235.3237	$235.32	$235.30	$235.30
Purchase #5	$70.51	11.141%	$78.3655	$78.37	$78.35	$78.40
Purchase #6	$170.32	8.552%	$184.8858	$184.89	$184.90	$184.90
Purchase #7	$113.83	8.355%	$123.3405	$123.34	$123.35	$123.30
7 purchase totals =	$892.10		$975.6333	$975.64	$975.60	$975.60