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	$59.91	7.710%	$64.5291	$64.53	$64.55	$64.50
Purchase #2	$40.94	12.382%	$46.0092	$46.01	$46.00	$46.00
Purchase #3	$245.54	13.170%	$277.8776	$277.88	$277.90	$277.90
Purchase #4	$202.31	7.661%	$217.809	$217.81	$217.80	$217.80
Purchase #5	$100.54	6.565%	$107.1405	$107.14	$107.15	$107.10
Purchase #6	$76.86	4.547%	$80.3548	$80.35	$80.35	$80.40
Purchase #7	$125.62	4.691%	$131.5128	$131.51	$131.50	$131.50
7 purchase totals =	$851.72		$925.2330	$925.23	$925.25	$925.20