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	$244.55	4.274%	$255.0021	$255.00	$255.00	$255.00
Purchase #2	$207.77	5.644%	$219.4965	$219.50	$219.50	$219.50
Purchase #3	$198.69	12.654%	$223.8322	$223.83	$223.85	$223.80
Purchase #4	$134.72	11.851%	$150.6857	$150.69	$150.70	$150.70
Purchase #5	$94.76	9.430%	$103.6959	$103.70	$103.70	$103.70
Purchase #6	$82.57	13.410%	$93.6426	$93.64	$93.65	$93.60
Purchase #7	$179.70	10.495%	$198.5595	$198.56	$198.55	$198.60
7 purchase totals =	$1,142.76		$1,244.9145	$1,244.92	$1,244.95	$1,244.90