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	$180.58	11.208%	$200.8194	$200.82	$200.80	$200.80
Purchase #2	$128.55	6.480%	$136.88	$136.88	$136.90	$136.90
Purchase #3	$114.94	8.222%	$124.3904	$124.39	$124.40	$124.40
Purchase #4	$211.79	11.205%	$235.5211	$235.52	$235.50	$235.50
Purchase #5	$229.37	9.661%	$251.5294	$251.53	$251.55	$251.50
Purchase #6	$186.54	13.371%	$211.4823	$211.48	$211.50	$211.50
Purchase #7	$42.61	5.538%	$44.9697	$44.97	$44.95	$45.00
7 purchase totals =	$1,094.38		$1,205.5923	$1,205.59	$1,205.60	$1,205.60