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	$123.89	9.259%	$135.361	$135.36	$135.35	$135.40
Purchase #2	$240.89	4.154%	$250.8966	$250.90	$250.90	$250.90
Purchase #3	$154.84	9.481%	$169.5204	$169.52	$169.50	$169.50
Purchase #4	$229.27	5.762%	$242.4805	$242.48	$242.50	$242.50
Purchase #5	$15.55	13.767%	$17.6908	$17.69	$17.70	$17.70
Purchase #6	$181.72	7.868%	$196.0177	$196.02	$196.00	$196.00
Purchase #7	$55.51	13.597%	$63.0577	$63.06	$63.05	$63.10
7 purchase totals =	$1,001.67		$1,075.0247	$1,075.03	$1,075.00	$1,075.10