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	$78.95	12.221%	$88.5985	$88.60	$88.60	$88.60
Purchase #2	$203.91	13.615%	$231.6723	$231.67	$231.65	$231.70
Purchase #3	$40.82	3.104%	$42.0871	$42.09	$42.10	$42.10
Purchase #4	$42.61	6.733%	$45.4789	$45.48	$45.50	$45.50
Purchase #5	$152.34	6.377%	$162.0547	$162.05	$162.05	$162.10
Purchase #6	$216.42	9.258%	$236.4562	$236.46	$236.45	$236.50
Purchase #7	$245.88	13.744%	$279.6737	$279.67	$279.65	$279.70
7 purchase totals =	$980.93		$1,086.0214	$1,086.02	$1,086.00	$1,086.20