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	$56.84	12.255%	$63.8057	$63.81	$63.80	$63.80
Purchase #2	$38.84	9.191%	$42.4098	$42.41	$42.40	$42.40
Purchase #3	$83.40	8.419%	$90.4214	$90.42	$90.40	$90.40
Purchase #4	$30.45	3.661%	$31.5648	$31.56	$31.55	$31.60
Purchase #5	$33.46	9.270%	$36.5617	$36.56	$36.55	$36.60
Purchase #6	$77.69	11.866%	$86.9087	$86.91	$86.90	$86.90
Purchase #7	$179.63	7.374%	$192.8759	$192.88	$192.90	$192.90
7 purchase totals =	$500.31		$544.5480	$544.55	$544.50	$544.60