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	$244.82	13.512%	$277.9001	$277.90	$277.90	$277.90
Purchase #2	$242.94	13.139%	$274.8599	$274.86	$274.85	$274.90
Purchase #3	$189.62	6.626%	$202.1842	$202.18	$202.20	$202.20
Purchase #4	$151.88	13.455%	$172.3155	$172.32	$172.30	$172.30
Purchase #5	$194.89	10.844%	$216.0239	$216.02	$216.00	$216.00
Purchase #6	$89.36	10.584%	$98.8179	$98.82	$98.80	$98.80
Purchase #7	$80.31	3.823%	$83.3803	$83.38	$83.40	$83.40
7 purchase totals =	$1,193.82		$1,325.4818	$1,325.48	$1,325.45	$1,325.50