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	$67.45	3.543%	$69.8398	$69.84	$69.85	$69.80
Purchase #2	$57.60	3.453%	$59.5889	$59.59	$59.60	$59.60
Purchase #3	$102.49	10.505%	$113.2566	$113.26	$113.25	$113.30
Purchase #4	$218.32	6.864%	$233.3055	$233.31	$233.30	$233.30
Purchase #5	$79.44	4.148%	$82.7352	$82.74	$82.75	$82.70
Purchase #6	$6.59	11.432%	$7.3434	$7.34	$7.35	$7.30
Purchase #7	$22.34	13.771%	$25.4164	$25.42	$25.40	$25.40
7 purchase totals =	$554.23		$591.4858	$591.50	$591.50	$591.40