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	$138.37	8.862%	$150.6323	$150.63	$150.65	$150.60
Purchase #2	$52.70	7.434%	$56.6177	$56.62	$56.60	$56.60
Purchase #3	$227.61	11.808%	$254.4862	$254.49	$254.50	$254.50
Purchase #4	$42.78	5.648%	$45.1962	$45.20	$45.20	$45.20
Purchase #5	$164.49	12.343%	$184.793	$184.79	$184.80	$184.80
Purchase #6	$142.73	11.700%	$159.4294	$159.43	$159.45	$159.40
Purchase #7	$174.60	9.649%	$191.4472	$191.45	$191.45	$191.40
7 purchase totals =	$943.28		$1,042.6020	$1,042.61	$1,042.65	$1,042.50