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	$159.70	12.427%	$179.5459	$179.55	$179.55	$179.50
Purchase #2	$166.39	11.415%	$185.3834	$185.38	$185.40	$185.40
Purchase #3	$20.43	9.190%	$22.3075	$22.31	$22.30	$22.30
Purchase #4	$101.86	11.190%	$113.2581	$113.26	$113.25	$113.30
Purchase #5	$133.82	12.106%	$150.0202	$150.02	$150.00	$150.00
Purchase #6	$220.55	4.816%	$231.1717	$231.17	$231.15	$231.20
Purchase #7	$185.80	12.250%	$208.5605	$208.56	$208.55	$208.60
7 purchase totals =	$988.55		$1,090.2473	$1,090.25	$1,090.20	$1,090.30