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	$91.38	12.605%	$102.8984	$102.90	$102.90	$102.90
Purchase #2	$71.92	12.491%	$80.9035	$80.90	$80.90	$80.90
Purchase #3	$113.40	7.532%	$121.9413	$121.94	$121.95	$121.90
Purchase #4	$94.42	6.533%	$100.5885	$100.59	$100.60	$100.60
Purchase #5	$28.38	10.718%	$31.4218	$31.42	$31.40	$31.40
Purchase #6	$106.36	12.477%	$119.6305	$119.63	$119.65	$119.60
Purchase #7	$157.33	5.471%	$165.9375	$165.94	$165.95	$165.90
7 purchase totals =	$663.19		$723.3215	$723.32	$723.35	$723.20