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	$46.43	10.262%	$51.1946	$51.19	$51.20	$51.20
Purchase #2	$39.31	3.757%	$40.7869	$40.79	$40.80	$40.80
Purchase #3	$84.69	6.170%	$89.9154	$89.92	$89.90	$89.90
Purchase #4	$163.29	9.849%	$179.3724	$179.37	$179.35	$179.40
Purchase #5	$141.73	7.420%	$152.2464	$152.25	$152.25	$152.20
Purchase #6	$162.76	6.508%	$173.3524	$173.35	$173.35	$173.40
Purchase #7	$231.96	7.457%	$249.2573	$249.26	$249.25	$249.30
7 purchase totals =	$870.17		$936.1254	$936.13	$936.10	$936.20