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	$240.65	12.848%	$271.5687	$271.57	$271.55	$271.60
Purchase #2	$109.79	13.770%	$124.9081	$124.91	$124.90	$124.90
Purchase #3	$170.73	12.189%	$191.5403	$191.54	$191.55	$191.50
Purchase #4	$176.96	7.108%	$189.5383	$189.54	$189.55	$189.50
Purchase #5	$11.87	7.155%	$12.7193	$12.72	$12.70	$12.70
Purchase #6	$248.28	7.807%	$267.6632	$267.66	$267.65	$267.70
Purchase #7	$87.55	5.676%	$92.5193	$92.52	$92.50	$92.50
7 purchase totals =	$1,045.83		$1,150.4572	$1,150.46	$1,150.40	$1,150.40