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	$28.87	10.688%	$31.9556	$31.96	$31.95	$32.00
Purchase #2	$15.81	9.190%	$17.2629	$17.26	$17.25	$17.30
Purchase #3	$112.92	10.818%	$125.1357	$125.14	$125.15	$125.10
Purchase #4	$128.55	12.579%	$144.7203	$144.72	$144.70	$144.70
Purchase #5	$179.25	11.788%	$200.38	$200.38	$200.40	$200.40
Purchase #6	$21.59	6.292%	$22.9484	$22.95	$22.95	$22.90
Purchase #7	$121.34	5.129%	$127.5635	$127.56	$127.55	$127.60
7 purchase totals =	$608.33		$669.9664	$669.97	$669.95	$670.00