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	$123.53	11.554%	$137.8027	$137.80	$137.80	$137.80
Purchase #2	$82.36	6.216%	$87.4795	$87.48	$87.50	$87.50
Purchase #3	$236.72	8.113%	$255.9251	$255.93	$255.95	$255.90
Purchase #4	$146.52	6.160%	$155.5456	$155.55	$155.55	$155.50
Purchase #5	$225.56	7.134%	$241.6515	$241.65	$241.65	$241.70
Purchase #6	$48.25	5.678%	$50.9896	$50.99	$51.00	$51.00
Purchase #7	$68.35	5.809%	$72.3205	$72.32	$72.30	$72.30
7 purchase totals =	$931.29		$1,001.7145	$1,001.72	$1,001.75	$1,001.70