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	$168.44	13.166%	$190.6168	$190.62	$190.60	$190.60
Purchase #2	$10.64	3.677%	$11.0312	$11.03	$11.05	$11.00
Purchase #3	$106.29	11.440%	$118.4496	$118.45	$118.45	$118.40
Purchase #4	$139.92	6.408%	$148.8861	$148.89	$148.90	$148.90
Purchase #5	$213.29	4.390%	$222.6534	$222.65	$222.65	$222.70
Purchase #6	$211.33	3.207%	$218.1074	$218.11	$218.10	$218.10
Purchase #7	$96.52	3.752%	$100.1414	$100.14	$100.15	$100.10
7 purchase totals =	$946.43		$1,009.8859	$1,009.89	$1,009.90	$1,009.80