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	$27.67	12.372%	$31.0933	$31.09	$31.10	$31.10
Purchase #2	$223.78	6.760%	$238.9075	$238.91	$238.90	$238.90
Purchase #3	$182.77	7.531%	$196.5344	$196.53	$196.55	$196.50
Purchase #4	$242.77	12.439%	$272.9682	$272.97	$272.95	$273.00
Purchase #5	$79.79	8.288%	$86.403	$86.40	$86.40	$86.40
Purchase #6	$28.35	11.784%	$31.6908	$31.69	$31.70	$31.70
Purchase #7	$96.60	13.187%	$109.3386	$109.34	$109.35	$109.30
7 purchase totals =	$881.73		$966.9358	$966.93	$966.95	$966.90