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	$127.27	3.487%	$131.7079	$131.71	$131.70	$131.70
Purchase #2	$86.31	4.750%	$90.4097	$90.41	$90.40	$90.40
Purchase #3	$172.93	8.121%	$186.9736	$186.97	$186.95	$187.00
Purchase #4	$214.35	12.205%	$240.5114	$240.51	$240.50	$240.50
Purchase #5	$23.91	8.399%	$25.9182	$25.92	$25.90	$25.90
Purchase #6	$100.55	10.470%	$111.0776	$111.08	$111.10	$111.10
Purchase #7	$230.70	4.212%	$240.4171	$240.42	$240.40	$240.40
7 purchase totals =	$956.02		$1,027.0155	$1,027.02	$1,026.95	$1,027.00