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	$234.60	3.280%	$242.2949	$242.29	$242.30	$242.30
Purchase #2	$164.74	6.158%	$174.8847	$174.88	$174.90	$174.90
Purchase #3	$113.61	8.719%	$123.5157	$123.52	$123.50	$123.50
Purchase #4	$43.37	12.138%	$48.6343	$48.63	$48.65	$48.60
Purchase #5	$116.66	11.574%	$130.1622	$130.16	$130.15	$130.20
Purchase #6	$144.53	4.254%	$150.6783	$150.68	$150.70	$150.70
Purchase #7	$65.55	9.870%	$72.0198	$72.02	$72.00	$72.00
7 purchase totals =	$883.06		$942.1899	$942.18	$942.20	$942.20