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	$29.41	11.702%	$32.8516	$32.85	$32.85	$32.90
Purchase #2	$17.64	12.566%	$19.8566	$19.86	$19.85	$19.90
Purchase #3	$188.54	10.859%	$209.0136	$209.01	$209.00	$209.00
Purchase #4	$203.76	5.793%	$215.5638	$215.56	$215.55	$215.60
Purchase #5	$35.79	13.134%	$40.4907	$40.49	$40.50	$40.50
Purchase #6	$38.82	7.140%	$41.5917	$41.59	$41.60	$41.60
Purchase #7	$136.50	8.269%	$147.7872	$147.79	$147.80	$147.80
7 purchase totals =	$650.46		$707.1552	$707.15	$707.15	$707.30