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	$166.94	11.744%	$186.5454	$186.55	$186.55	$186.50
Purchase #2	$100.29	3.463%	$103.763	$103.76	$103.75	$103.80
Purchase #3	$196.46	9.440%	$215.0058	$215.01	$215.00	$215.00
Purchase #4	$218.33	9.514%	$239.1019	$239.10	$239.10	$239.10
Purchase #5	$55.35	12.585%	$62.3158	$62.32	$62.30	$62.30
Purchase #6	$90.40	11.842%	$101.1052	$101.11	$101.10	$101.10
Purchase #7	$47.50	13.329%	$53.8313	$53.83	$53.85	$53.80
7 purchase totals =	$875.27		$961.6684	$961.68	$961.65	$961.60