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	$81.29	11.216%	$90.4075	$90.41	$90.40	$90.40
Purchase #2	$29.96	4.420%	$31.2842	$31.28	$31.30	$31.30
Purchase #3	$31.31	10.568%	$34.6188	$34.62	$34.60	$34.60
Purchase #4	$98.56	13.183%	$111.5532	$111.55	$111.55	$111.60
Purchase #5	$203.94	11.644%	$227.6868	$227.69	$227.70	$227.70
Purchase #6	$109.60	3.625%	$113.573	$113.57	$113.55	$113.60
Purchase #7	$78.39	7.164%	$84.0059	$84.01	$84.00	$84.00
7 purchase totals =	$633.05		$693.1294	$693.13	$693.10	$693.20