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	$212.33	12.752%	$239.4063	$239.41	$239.40	$239.40
Purchase #2	$246.86	9.155%	$269.46	$269.46	$269.45	$269.50
Purchase #3	$50.50	9.577%	$55.3364	$55.34	$55.35	$55.30
Purchase #4	$186.60	12.457%	$209.8448	$209.84	$209.85	$209.80
Purchase #5	$90.92	5.479%	$95.9015	$95.90	$95.90	$95.90
Purchase #6	$179.91	9.795%	$197.5322	$197.53	$197.55	$197.50
Purchase #7	$17.32	12.360%	$19.4608	$19.46	$19.45	$19.50
7 purchase totals =	$984.44		$1,086.9420	$1,086.94	$1,086.95	$1,086.90