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	$210.26	12.480%	$236.5004	$236.50	$236.50	$236.50
Purchase #2	$172.90	10.616%	$191.2551	$191.26	$191.25	$191.30
Purchase #3	$193.84	7.848%	$209.0526	$209.05	$209.05	$209.10
Purchase #4	$19.53	10.671%	$21.614	$21.61	$21.60	$21.60
Purchase #5	$156.72	13.873%	$178.4618	$178.46	$178.45	$178.50
Purchase #6	$21.33	8.629%	$23.1706	$23.17	$23.15	$23.20
Purchase #7	$135.25	6.709%	$144.3239	$144.32	$144.30	$144.30
7 purchase totals =	$909.83		$1,004.3784	$1,004.37	$1,004.30	$1,004.50