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	$28.42	3.267%	$29.3485	$29.35	$29.35	$29.30
Purchase #2	$98.26	7.470%	$105.6	$105.60	$105.60	$105.60
Purchase #3	$5.90	8.609%	$6.4079	$6.41	$6.40	$6.40
Purchase #4	$82.47	10.198%	$90.8803	$90.88	$90.90	$90.90
Purchase #5	$95.29	4.288%	$99.376	$99.38	$99.40	$99.40
Purchase #6	$95.38	13.791%	$108.5339	$108.53	$108.55	$108.50
Purchase #7	$70.35	12.702%	$79.2859	$79.29	$79.30	$79.30
7 purchase totals =	$476.07		$519.4325	$519.44	$519.50	$519.40