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	$124.81	10.148%	$137.4757	$137.48	$137.50	$137.50
Purchase #2	$249.93	13.874%	$284.6053	$284.61	$284.60	$284.60
Purchase #3	$27.33	12.596%	$30.7725	$30.77	$30.75	$30.80
Purchase #4	$28.99	11.458%	$32.3117	$32.31	$32.30	$32.30
Purchase #5	$114.97	7.191%	$123.2375	$123.24	$123.25	$123.20
Purchase #6	$134.60	9.230%	$147.0236	$147.02	$147.00	$147.00
Purchase #7	$220.93	13.232%	$250.1635	$250.16	$250.15	$250.20
7 purchase totals =	$901.56		$1,005.5898	$1,005.59	$1,005.55	$1,005.60