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	$93.38	10.427%	$103.1167	$103.12	$103.10	$103.10
Purchase #2	$125.60	13.244%	$142.2345	$142.23	$142.25	$142.20
Purchase #3	$67.45	7.636%	$72.6005	$72.60	$72.60	$72.60
Purchase #4	$47.44	5.157%	$49.8865	$49.89	$49.90	$49.90
Purchase #5	$22.25	12.772%	$25.0918	$25.09	$25.10	$25.10
Purchase #6	$162.85	3.444%	$168.4586	$168.46	$168.45	$168.50
Purchase #7	$56.67	5.734%	$59.9195	$59.92	$59.90	$59.90
7 purchase totals =	$575.64		$621.3081	$621.31	$621.30	$621.30