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	$134.32	4.513%	$140.3819	$140.38	$140.40	$140.40
Purchase #2	$204.56	6.131%	$217.1016	$217.10	$217.10	$217.10
Purchase #3	$71.59	9.622%	$78.4784	$78.48	$78.50	$78.50
Purchase #4	$87.63	11.839%	$98.0045	$98.00	$98.00	$98.00
Purchase #5	$62.82	11.794%	$70.229	$70.23	$70.25	$70.20
Purchase #6	$105.25	3.556%	$108.9927	$108.99	$109.00	$109.00
Purchase #7	$160.51	3.504%	$166.1343	$166.13	$166.15	$166.10
7 purchase totals =	$826.68		$879.3224	$879.31	$879.40	$879.30