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	$106.50	12.150%	$119.4398	$119.44	$119.45	$119.40
Purchase #2	$229.86	11.166%	$255.5262	$255.53	$255.55	$255.50
Purchase #3	$79.88	8.502%	$86.6714	$86.67	$86.65	$86.70
Purchase #4	$225.41	4.341%	$235.195	$235.20	$235.20	$235.20
Purchase #5	$64.52	4.684%	$67.5421	$67.54	$67.55	$67.50
Purchase #6	$147.98	4.222%	$154.2277	$154.23	$154.25	$154.20
Purchase #7	$147.46	6.397%	$156.893	$156.89	$156.90	$156.90
7 purchase totals =	$1,001.61		$1,075.4952	$1,075.50	$1,075.55	$1,075.40