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	$59.97	12.184%	$67.2767	$67.28	$67.30	$67.30
Purchase #2	$137.70	6.166%	$146.1906	$146.19	$146.20	$146.20
Purchase #3	$35.60	12.869%	$40.1814	$40.18	$40.20	$40.20
Purchase #4	$70.96	13.256%	$80.3665	$80.37	$80.35	$80.40
Purchase #5	$192.89	10.590%	$213.3171	$213.32	$213.30	$213.30
Purchase #6	$131.80	10.354%	$145.4466	$145.45	$145.45	$145.40
Purchase #7	$87.28	6.178%	$92.6722	$92.67	$92.65	$92.70
7 purchase totals =	$716.20		$785.4511	$785.46	$785.45	$785.50