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	$88.75	3.407%	$91.7737	$91.77	$91.75	$91.80
Purchase #2	$104.25	12.296%	$117.0686	$117.07	$117.05	$117.10
Purchase #3	$84.52	4.258%	$88.1189	$88.12	$88.10	$88.10
Purchase #4	$76.37	5.318%	$80.4314	$80.43	$80.45	$80.40
Purchase #5	$91.33	11.502%	$101.8348	$101.83	$101.85	$101.80
Purchase #6	$127.35	3.584%	$131.9142	$131.91	$131.90	$131.90
Purchase #7	$69.39	12.861%	$78.3142	$78.31	$78.30	$78.30
7 purchase totals =	$641.96		$689.4558	$689.44	$689.40	$689.40