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	$102.64	6.538%	$109.3506	$109.35	$109.35	$109.40
Purchase #2	$165.39	12.548%	$186.1431	$186.14	$186.15	$186.10
Purchase #3	$168.80	8.368%	$182.9252	$182.93	$182.95	$182.90
Purchase #4	$189.76	8.704%	$206.2767	$206.28	$206.30	$206.30
Purchase #5	$83.34	12.624%	$93.8608	$93.86	$93.85	$93.90
Purchase #6	$246.28	6.575%	$262.4729	$262.47	$262.45	$262.50
Purchase #7	$144.27	7.739%	$155.4351	$155.44	$155.45	$155.40
7 purchase totals =	$1,100.48		$1,196.4644	$1,196.47	$1,196.50	$1,196.50