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	$44.60	6.725%	$47.5994	$47.60	$47.60	$47.60
Purchase #2	$53.79	4.463%	$56.1906	$56.19	$56.20	$56.20
Purchase #3	$113.35	6.557%	$120.7824	$120.78	$120.80	$120.80
Purchase #4	$94.61	3.780%	$98.1863	$98.19	$98.20	$98.20
Purchase #5	$41.56	3.137%	$42.8637	$42.86	$42.85	$42.90
Purchase #6	$57.42	11.261%	$63.8861	$63.89	$63.90	$63.90
Purchase #7	$148.78	9.410%	$162.7802	$162.78	$162.80	$162.80
7 purchase totals =	$554.11		$592.2887	$592.29	$592.35	$592.40