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	$192.53	3.320%	$198.922	$198.92	$198.90	$198.90
Purchase #2	$115.81	9.743%	$127.0934	$127.09	$127.10	$127.10
Purchase #3	$52.75	10.644%	$58.3647	$58.36	$58.35	$58.40
Purchase #4	$39.71	6.850%	$42.4301	$42.43	$42.45	$42.40
Purchase #5	$178.25	10.430%	$196.8415	$196.84	$196.85	$196.80
Purchase #6	$202.82	7.840%	$218.7211	$218.72	$218.70	$218.70
Purchase #7	$136.60	6.409%	$145.3547	$145.35	$145.35	$145.40
7 purchase totals =	$918.47		$987.7275	$987.71	$987.70	$987.70