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	$131.73	9.539%	$144.2957	$144.30	$144.30	$144.30
Purchase #2	$98.50	5.207%	$103.6289	$103.63	$103.65	$103.60
Purchase #3	$36.29	3.557%	$37.5808	$37.58	$37.60	$37.60
Purchase #4	$106.29	12.325%	$119.3902	$119.39	$119.40	$119.40
Purchase #5	$99.61	3.529%	$103.1252	$103.13	$103.15	$103.10
Purchase #6	$148.63	8.610%	$161.427	$161.43	$161.45	$161.40
Purchase #7	$61.89	12.858%	$69.8478	$69.85	$69.85	$69.80
7 purchase totals =	$682.94		$739.2956	$739.31	$739.40	$739.20