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	$115.98	6.509%	$123.5291	$123.53	$123.55	$123.50
Purchase #2	$228.38	12.305%	$256.4822	$256.48	$256.50	$256.50
Purchase #3	$134.66	9.551%	$147.5214	$147.52	$147.50	$147.50
Purchase #4	$224.66	13.642%	$255.3081	$255.31	$255.30	$255.30
Purchase #5	$209.27	13.387%	$237.285	$237.29	$237.30	$237.30
Purchase #6	$134.29	12.435%	$150.989	$150.99	$151.00	$151.00
Purchase #7	$149.91	4.571%	$156.7624	$156.76	$156.75	$156.80
7 purchase totals =	$1,197.15		$1,327.8772	$1,327.88	$1,327.90	$1,327.90