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	$33.83	10.838%	$37.4965	$37.50	$37.50	$37.50
Purchase #2	$40.84	8.747%	$44.4123	$44.41	$44.40	$44.40
Purchase #3	$91.31	10.312%	$100.7259	$100.73	$100.75	$100.70
Purchase #4	$54.97	13.626%	$62.4602	$62.46	$62.45	$62.50
Purchase #5	$164.34	3.254%	$169.6876	$169.69	$169.70	$169.70
Purchase #6	$119.71	10.424%	$132.1886	$132.19	$132.20	$132.20
Purchase #7	$79.61	4.134%	$82.9011	$82.90	$82.90	$82.90
7 purchase totals =	$584.61		$629.8722	$629.88	$629.90	$629.90