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	$242.39	12.851%	$273.5395	$273.54	$273.55	$273.50
Purchase #2	$89.91	5.872%	$95.1895	$95.19	$95.20	$95.20
Purchase #3	$22.77	5.397%	$23.9989	$24.00	$24.00	$24.00
Purchase #4	$137.89	7.532%	$148.2759	$148.28	$148.30	$148.30
Purchase #5	$27.57	10.311%	$30.4127	$30.41	$30.40	$30.40
Purchase #6	$94.30	6.392%	$100.3277	$100.33	$100.35	$100.30
Purchase #7	$62.92	4.718%	$65.8886	$65.89	$65.90	$65.90
7 purchase totals =	$677.75		$737.6328	$737.64	$737.70	$737.60