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	$83.50	13.441%	$94.7232	$94.72	$94.70	$94.70
Purchase #2	$168.43	12.163%	$188.9161	$188.92	$188.90	$188.90
Purchase #3	$20.43	6.790%	$21.8172	$21.82	$21.80	$21.80
Purchase #4	$18.42	6.807%	$19.6738	$19.67	$19.65	$19.70
Purchase #5	$55.82	6.116%	$59.234	$59.23	$59.25	$59.20
Purchase #6	$94.78	10.557%	$104.7859	$104.79	$104.80	$104.80
Purchase #7	$175.48	3.180%	$181.0603	$181.06	$181.05	$181.10
7 purchase totals =	$616.86		$670.2105	$670.21	$670.15	$670.20