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	$59.90	12.744%	$67.5337	$67.53	$67.55	$67.50
Purchase #2	$199.43	7.124%	$213.6374	$213.64	$213.65	$213.60
Purchase #3	$228.89	11.109%	$254.3174	$254.32	$254.30	$254.30
Purchase #4	$244.54	8.751%	$265.9397	$265.94	$265.95	$265.90
Purchase #5	$228.62	3.724%	$237.1338	$237.13	$237.15	$237.10
Purchase #6	$197.61	10.610%	$218.5764	$218.58	$218.60	$218.60
Purchase #7	$34.78	8.372%	$37.6918	$37.69	$37.70	$37.70
7 purchase totals =	$1,193.77		$1,294.8302	$1,294.83	$1,294.90	$1,294.70