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	$112.40	4.788%	$117.7817	$117.78	$117.80	$117.80
Purchase #2	$102.76	3.477%	$106.333	$106.33	$106.35	$106.30
Purchase #3	$120.85	10.538%	$133.5852	$133.59	$133.60	$133.60
Purchase #4	$60.72	12.650%	$68.4011	$68.40	$68.40	$68.40
Purchase #5	$196.57	13.203%	$222.5231	$222.52	$222.50	$222.50
Purchase #6	$12.89	12.731%	$14.531	$14.53	$14.55	$14.50
Purchase #7	$179.79	11.398%	$200.2825	$200.28	$200.30	$200.30
7 purchase totals =	$785.98		$863.4376	$863.43	$863.50	$863.40