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	$189.63	11.117%	$210.7112	$210.71	$210.70	$210.70
Purchase #2	$239.71	4.483%	$250.4562	$250.46	$250.45	$250.50
Purchase #3	$39.78	9.447%	$43.538	$43.54	$43.55	$43.50
Purchase #4	$213.48	11.500%	$238.0302	$238.03	$238.05	$238.00
Purchase #5	$116.26	3.408%	$120.2221	$120.22	$120.20	$120.20
Purchase #6	$48.56	3.850%	$50.4296	$50.43	$50.45	$50.40
Purchase #7	$131.88	9.250%	$144.0789	$144.08	$144.10	$144.10
7 purchase totals =	$979.30		$1,057.4662	$1,057.47	$1,057.50	$1,057.40