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	$184.79	3.293%	$190.8751	$190.88	$190.90	$190.90
Purchase #2	$75.26	10.200%	$82.9365	$82.94	$82.95	$82.90
Purchase #3	$229.62	10.443%	$253.5992	$253.60	$253.60	$253.60
Purchase #4	$250.40	7.465%	$269.0924	$269.09	$269.10	$269.10
Purchase #5	$198.55	13.720%	$225.7911	$225.79	$225.80	$225.80
Purchase #6	$248.43	6.861%	$265.4748	$265.47	$265.45	$265.50
Purchase #7	$91.83	7.616%	$98.8238	$98.82	$98.80	$98.80
7 purchase totals =	$1,278.88		$1,386.5929	$1,386.59	$1,386.60	$1,386.60