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	$37.95	12.443%	$42.6721	$42.67	$42.65	$42.70
Purchase #2	$220.39	13.374%	$249.865	$249.87	$249.85	$249.90
Purchase #3	$5.72	4.529%	$5.9791	$5.98	$6.00	$6.00
Purchase #4	$198.46	6.771%	$211.8977	$211.90	$211.90	$211.90
Purchase #5	$250.97	4.774%	$262.9513	$262.95	$262.95	$263.00
Purchase #6	$130.50	11.181%	$145.0912	$145.09	$145.10	$145.10
Purchase #7	$91.70	7.374%	$98.462	$98.46	$98.45	$98.50
7 purchase totals =	$935.69		$1,016.9184	$1,016.92	$1,016.90	$1,017.10