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	$23.29	8.795%	$25.3384	$25.34	$25.35	$25.30
Purchase #2	$199.30	11.787%	$222.7915	$222.79	$222.80	$222.80
Purchase #3	$42.69	3.626%	$44.2379	$44.24	$44.25	$44.20
Purchase #4	$227.70	7.240%	$244.1855	$244.19	$244.20	$244.20
Purchase #5	$66.59	9.469%	$72.8954	$72.90	$72.90	$72.90
Purchase #6	$86.61	5.639%	$91.4939	$91.49	$91.50	$91.50
Purchase #7	$144.72	4.109%	$150.6665	$150.67	$150.65	$150.70
7 purchase totals =	$790.90		$851.6091	$851.62	$851.65	$851.60