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	$171.35	9.152%	$187.032	$187.03	$187.05	$187.00
Purchase #2	$213.94	3.195%	$220.7754	$220.78	$220.80	$220.80
Purchase #3	$172.40	5.797%	$182.394	$182.39	$182.40	$182.40
Purchase #4	$179.31	13.819%	$204.0888	$204.09	$204.10	$204.10
Purchase #5	$27.91	13.407%	$31.6519	$31.65	$31.65	$31.70
Purchase #6	$154.76	5.230%	$162.8539	$162.85	$162.85	$162.90
Purchase #7	$102.55	9.256%	$112.042	$112.04	$112.05	$112.00
7 purchase totals =	$1,022.22		$1,100.8380	$1,100.83	$1,100.90	$1,100.90