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	$179.98	5.279%	$189.4811	$189.48	$189.50	$189.50
Purchase #2	$117.47	8.379%	$127.3128	$127.31	$127.30	$127.30
Purchase #3	$106.39	11.850%	$118.9972	$119.00	$119.00	$119.00
Purchase #4	$36.28	4.427%	$37.8861	$37.89	$37.90	$37.90
Purchase #5	$101.42	12.601%	$114.1999	$114.20	$114.20	$114.20
Purchase #6	$120.35	9.195%	$131.4162	$131.42	$131.40	$131.40
Purchase #7	$34.86	3.325%	$36.0191	$36.02	$36.00	$36.00
7 purchase totals =	$696.75		$755.3124	$755.32	$755.30	$755.30