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	$7.64	11.391%	$8.5103	$8.51	$8.50	$8.50
Purchase #2	$33.96	10.323%	$37.4657	$37.47	$37.45	$37.50
Purchase #3	$157.65	9.228%	$172.1979	$172.20	$172.20	$172.20
Purchase #4	$162.59	13.212%	$184.0714	$184.07	$184.05	$184.10
Purchase #5	$158.81	10.498%	$175.4819	$175.48	$175.50	$175.50
Purchase #6	$109.36	12.687%	$123.2345	$123.23	$123.25	$123.20
Purchase #7	$225.88	6.813%	$241.2692	$241.27	$241.25	$241.30
7 purchase totals =	$855.89		$942.2309	$942.23	$942.20	$942.30