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	$64.63	12.724%	$72.8535	$72.85	$72.85	$72.90
Purchase #2	$234.61	12.649%	$264.2858	$264.29	$264.30	$264.30
Purchase #3	$172.78	5.554%	$182.3762	$182.38	$182.40	$182.40
Purchase #4	$136.67	5.797%	$144.5928	$144.59	$144.60	$144.60
Purchase #5	$70.80	12.359%	$79.5502	$79.55	$79.55	$79.60
Purchase #6	$28.75	12.571%	$32.3642	$32.36	$32.35	$32.40
Purchase #7	$115.32	8.412%	$125.0207	$125.02	$125.00	$125.00
7 purchase totals =	$823.56		$901.0434	$901.04	$901.05	$901.20