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	$250.89	12.160%	$281.3982	$281.40	$281.40	$281.40
Purchase #2	$43.85	6.844%	$46.8511	$46.85	$46.85	$46.90
Purchase #3	$140.72	13.490%	$159.7031	$159.70	$159.70	$159.70
Purchase #4	$237.50	11.538%	$264.9028	$264.90	$264.90	$264.90
Purchase #5	$184.89	4.691%	$193.5632	$193.56	$193.55	$193.60
Purchase #6	$154.33	13.133%	$174.5982	$174.60	$174.60	$174.60
Purchase #7	$42.86	5.558%	$45.2422	$45.24	$45.25	$45.20
7 purchase totals =	$1,055.04		$1,166.2588	$1,166.25	$1,166.25	$1,166.30