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	$144.72	3.558%	$149.8691	$149.87	$149.85	$149.90
Purchase #2	$67.90	6.619%	$72.3943	$72.39	$72.40	$72.40
Purchase #3	$146.82	5.304%	$154.6073	$154.61	$154.60	$154.60
Purchase #4	$249.32	9.514%	$273.0403	$273.04	$273.05	$273.00
Purchase #5	$84.47	11.668%	$94.326	$94.33	$94.35	$94.30
Purchase #6	$32.44	7.538%	$34.8853	$34.89	$34.90	$34.90
Purchase #7	$231.79	12.324%	$260.3558	$260.36	$260.35	$260.40
7 purchase totals =	$957.46		$1,039.4781	$1,039.49	$1,039.50	$1,039.50