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	$222.29	4.167%	$231.5528	$231.55	$231.55	$231.60
Purchase #2	$248.87	10.157%	$274.1477	$274.15	$274.15	$274.10
Purchase #3	$42.97	5.385%	$45.2839	$45.28	$45.30	$45.30
Purchase #4	$144.32	7.322%	$154.8871	$154.89	$154.90	$154.90
Purchase #5	$110.83	3.668%	$114.8952	$114.90	$114.90	$114.90
Purchase #6	$42.70	12.115%	$47.8731	$47.87	$47.85	$47.90
Purchase #7	$215.53	4.371%	$224.9508	$224.95	$224.95	$225.00
7 purchase totals =	$1,027.51		$1,093.5906	$1,093.59	$1,093.60	$1,093.70