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	$174.64	7.296%	$187.3817	$187.38	$187.40	$187.40
Purchase #2	$157.55	9.674%	$172.7914	$172.79	$172.80	$172.80
Purchase #3	$239.67	12.794%	$270.3334	$270.33	$270.35	$270.30
Purchase #4	$58.99	10.321%	$65.0784	$65.08	$65.10	$65.10
Purchase #5	$170.44	6.782%	$181.9992	$182.00	$182.00	$182.00
Purchase #6	$106.48	7.500%	$114.466	$114.47	$114.45	$114.50
Purchase #7	$183.89	6.840%	$196.4681	$196.47	$196.45	$196.50
7 purchase totals =	$1,091.66		$1,188.5182	$1,188.52	$1,188.55	$1,188.60