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	$52.83	9.540%	$57.87	$57.87	$57.85	$57.90
Purchase #2	$72.97	12.543%	$82.1226	$82.12	$82.10	$82.10
Purchase #3	$60.75	3.614%	$62.9455	$62.95	$62.95	$62.90
Purchase #4	$202.27	3.309%	$208.9631	$208.96	$208.95	$209.00
Purchase #5	$133.95	6.450%	$142.5898	$142.59	$142.60	$142.60
Purchase #6	$5.42	8.599%	$5.8861	$5.89	$5.90	$5.90
Purchase #7	$114.83	3.835%	$119.2337	$119.23	$119.25	$119.20
7 purchase totals =	$643.02		$679.6108	$679.61	$679.60	$679.60