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	$137.32	3.590%	$142.2498	$142.25	$142.25	$142.20
Purchase #2	$216.48	9.124%	$236.2316	$236.23	$236.25	$236.20
Purchase #3	$240.84	11.451%	$268.4186	$268.42	$268.40	$268.40
Purchase #4	$180.26	3.798%	$187.1063	$187.11	$187.10	$187.10
Purchase #5	$36.55	11.165%	$40.6308	$40.63	$40.65	$40.60
Purchase #6	$116.60	9.710%	$127.9219	$127.92	$127.90	$127.90
Purchase #7	$44.45	6.462%	$47.3224	$47.32	$47.30	$47.30
7 purchase totals =	$972.50		$1,049.8814	$1,049.88	$1,049.85	$1,049.70