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	$155.46	12.480%	$174.8614	$174.86	$174.85	$174.90
Purchase #2	$186.49	6.425%	$198.472	$198.47	$198.45	$198.50
Purchase #3	$26.85	5.193%	$28.2443	$28.24	$28.25	$28.20
Purchase #4	$67.35	4.579%	$70.434	$70.43	$70.45	$70.40
Purchase #5	$193.89	3.301%	$200.2903	$200.29	$200.30	$200.30
Purchase #6	$174.43	4.271%	$181.8799	$181.88	$181.90	$181.90
Purchase #7	$192.34	5.744%	$203.388	$203.39	$203.40	$203.40
7 purchase totals =	$996.81		$1,057.5699	$1,057.56	$1,057.60	$1,057.60