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	$33.46	3.308%	$34.5669	$34.57	$34.55	$34.60
Purchase #2	$85.29	7.498%	$91.685	$91.69	$91.70	$91.70
Purchase #3	$123.28	13.124%	$139.4593	$139.46	$139.45	$139.50
Purchase #4	$217.65	9.745%	$238.86	$238.86	$238.85	$238.90
Purchase #5	$98.70	4.811%	$103.4485	$103.45	$103.45	$103.40
Purchase #6	$161.40	8.590%	$175.2643	$175.26	$175.25	$175.30
Purchase #7	$151.40	12.230%	$169.9162	$169.92	$169.90	$169.90
7 purchase totals =	$871.18		$953.2002	$953.21	$953.15	$953.30