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	$13.69	11.200%	$15.2233	$15.22	$15.20	$15.20
Purchase #2	$78.32	4.605%	$81.9266	$81.93	$81.95	$81.90
Purchase #3	$213.35	5.840%	$225.8096	$225.81	$225.80	$225.80
Purchase #4	$186.73	12.278%	$209.6567	$209.66	$209.65	$209.70
Purchase #5	$72.48	8.263%	$78.469	$78.47	$78.45	$78.50
Purchase #6	$174.27	4.181%	$181.5562	$181.56	$181.55	$181.60
Purchase #7	$204.92	8.740%	$222.83	$222.83	$222.85	$222.80
7 purchase totals =	$943.76		$1,015.4714	$1,015.48	$1,015.45	$1,015.50