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	$230.87	10.391%	$254.8597	$254.86	$254.85	$254.90
Purchase #2	$30.99	7.187%	$33.2173	$33.22	$33.20	$33.20
Purchase #3	$169.44	6.560%	$180.5553	$180.56	$180.55	$180.60
Purchase #4	$178.89	13.395%	$202.8523	$202.85	$202.85	$202.90
Purchase #5	$202.83	7.372%	$217.7826	$217.78	$217.80	$217.80
Purchase #6	$137.82	4.649%	$144.2273	$144.23	$144.25	$144.20
Purchase #7	$38.86	10.294%	$42.8602	$42.86	$42.85	$42.90
7 purchase totals =	$989.70		$1,076.3547	$1,076.36	$1,076.35	$1,076.50