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	$25.80	4.501%	$26.9613	$26.96	$26.95	$27.00
Purchase #2	$89.63	12.134%	$100.5057	$100.51	$100.50	$100.50
Purchase #3	$229.60	11.300%	$255.5448	$255.54	$255.55	$255.50
Purchase #4	$236.66	6.133%	$251.1744	$251.17	$251.15	$251.20
Purchase #5	$192.45	5.129%	$202.3208	$202.32	$202.30	$202.30
Purchase #6	$121.57	10.116%	$133.868	$133.87	$133.85	$133.90
Purchase #7	$77.56	10.655%	$85.824	$85.82	$85.80	$85.80
7 purchase totals =	$973.27		$1,056.1990	$1,056.19	$1,056.10	$1,056.20